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Article

Reference Values of the Quality of Life after Brain Injury (QOLIBRI) from a General Population Sample in Italy

1
Institute of Medical Psychology and Medical Sociology, University Medical Center Göttingen, Waldweg 37A, 37073 Göttingen, Germany
2
Department of Public Health, Erasmus MC, University Medical Center Rotterdam, 3000 CA Rotterdam, The Netherlands
*
Author to whom correspondence should be addressed.
Membership of CENTER-TBI Participants and Investigators is provided in the Supplementary Materials.
J. Clin. Med. 2023, 12(2), 491; https://doi.org/10.3390/jcm12020491
Submission received: 21 October 2022 / Revised: 7 December 2022 / Accepted: 3 January 2023 / Published: 6 January 2023
(This article belongs to the Special Issue Traumatic Brain Injury (TBI): Recent Trends and Future Perspectives)

Abstract

:
Traumatic brain injury (TBI) may affect the lives of the individuals concerned and their relatives negatively in many dimensions. Health-related quality of life (HRQoL) is a comprehensive and complex concept that can assess one’s satisfaction with a broad range of areas of life and health. The Quality of Life after Traumatic Brain Injury (QOLIBRI) questionnaire is a TBI-specific measure for HRQoL which is used in research and health services worldwide. When evaluating self-reported HRQoL after TBI, reference values from a general population are helpful to perform clinically relevant evaluations and decisions about the condition of an affected person by comparing the patient scores with reference values. Despite the widespread use of the QOLIBRI, reference values have until now only been available for the Netherlands and the United Kingdom. The aim of this study was to validate the QOLIBRI for the general population in Italy and to provide reference values. An adapted form of the QOLIBRI was administered to 3298 Italians from a healthy general population using an online survey. Their scores were compared with those of 298 individuals post-TBI recruited within the international longitudinal observational cohort CENTER-TBI study in Italian hospitals, who completed the original questionnaire. The psychometric characteristics and the measurement invariance of the QOLIBRI were assessed. A regression analysis was performed to identify predictors relevant for HRQoL in the general population. Reference values were provided using percentiles. Measurement invariance analysis showed that the QOLIBRI captures the same HRQoL constructs in an Italian general population and Italian TBI sample from the observational Center-TBI study. Higher age, higher education and the absence of a chronic health condition were associated with higher QOLIBRI scores, suggesting better HRQoL. Reference values were provided for a general Italian population adjusted for age, sex, education and presence of chronic health conditions. We recommend using these for a better interpretation of the QOLIBRI score in clinical practice and research in Italy.

1. Introduction

Traumatic brain injury (TBI) is an important cause of burden of disease worldwide, as more than 50 million people acquire it every year [1]. In a study published in 2018, Dewan et al. [2] estimated that approximately 69 million people worldwide experience TBI each year. In Italy, the incidence of TBI varies from 212.4 [3] to 848 [4,5] cases per 100,000, depending on the study, placing it among the countries with the highest TBI rates in Europe.
TBI negatively affects the lives of individuals after TBI and their relatives [6,7] by limiting their everyday lives, causing physical [8], cognitive [9] and psychological problems [10], and having negative effects on their emotions [11] and social lives [12,13]. Because of the long-term outcomes, which are similar to those caused by a chronic health condition, TBI has been equated with chronic diseases [14]. In recent decades, the description and treatment of chronic diseases has seen a shift from a biomedical to a biopsychosocial approach to disease and health. Consequently, health is seen as a multidimensional construct that includes physical and psychosocial aspects [15]. In their systematic review, Polinder et al. [16] point out that TBI has a relevant impact on the health-related quality of life (HRQoL) of the individuals concerned.
HRQoL is a comprehensive and complex construct which includes a broad range of areas of life and health. It covers self-reported outcomes on health status and well-being, and can be used to determine the effectiveness of a treatment [16,17]. Sherer and his colleagues [18] postulated that physical function, physical symptoms, cognition, negative and positive emotions, sense of self, and social participation provide a differentiated foundation for understanding the HRQoL of individuals after TBI. HRQoL can be assessed using disease-specific or generic instruments. Generic instruments can be used in the assessment of HRQoL after TBI [19], especially when comparisons are to be made with other diseases [20]. However, these instruments are described as being less sensitive to specific health conditions, which is why the use of disease-specific instruments is recommended [21,22]. Specific instruments are generally more sensitive and more responsive [23] to the problems of a particular disease area and can capture HRQoL more precisely [24]. For example, Harfmann et al. [19] have compared specific and generic instruments in patients after TBI and shown that the TBI-specific measures offer a more detailed assessment of symptoms relevant to TBI than generic ones.
The instrument measuring Quality of Life after Traumatic Brain Injury (QOLIBRI) is the first disease-specific questionnaire that captures HRQoL after TBI [25,26]. It covers all aspects suggested by Sherer et al. [18] within 37 items forming six subscales (cognition, self, autonomy and daily life, social, emotions, physical). The QOLIBRI helps to identify self-perceived deficits that should be further investigated and, if possible, improved. This instrument was developed in 2010 and was validated for the Italian language in 2014 [27], showing good psychometric characteristics.
The QOLIBRI instrument is applied in various settings in the area of TBI, from international research studies to clinical use [28,29,30] and rehabilitation [31]. Until now the QOLIBRI has been translated and validated in more than 26 languages and is widely used internationally for individuals after TBI [31,32,33,34]. However, to better understand the clinical impact of TBI on the HRQoL of patients, reference values for individuals from comparable general populations are required. Reference values are important, e.g., in order to evaluate the HRQoL of an individual after TBI in relation to a comparable general population, so as to capture the HRQoL domains showing deficits. To date, no reference values exist for the Italian version of the QOLIBRI.
Since the QOLIBRI is a TBI-specific measure, it should be adapted for use in the general population. To ensure comparability of the QOLIBRI scores between individuals after TBI and the general population, evidence of measurement invariance (MI) is crucial. MI in this sense means that any observable variation in (adapted) QOLIBRI responses between TBI and the general population can be attributed to real differences in HRQoL. The aim of this study was therefore to validate the QOLIBRI questionnaire for a sample from the Italian general population in order to compile reference values and to compare these with the QOLIBRI scores of individuals after TBI.

2. Methods

2.1. Study Design

This study includes data from two different sources. Data for the general population sample from Italy are derived from a web-based, self-reported, cross-sectional study. The data for individuals after TBI stem from the multicenter, prospective, longitudinal, observational Collaborative European Neuro Trauma Effectiveness Research in Traumatic Brain Injury study (CENTER-TBI; clinicaltrials.gov NCT02210221). For details on enrollment of participants and recruitment, see Steyerberg et al. [35].

2.2. Ethical Approvals

2.2.1. General Population Sample

The study on general population was a part of the CENTER-TBI project. Ethical approval was obtained from the Leids Universitair Centrum—Commissie Medische Ethiek (approval P14.222/NV/nv, 3 December 2014).

2.2.2. TBI Sample

The CENTER-TBI study (EC grant 602150) has been conducted in accordance with all relevant laws of the EU if directly applicable or of direct effect and all relevant laws of the country where the recruiting sites were located, including, but not limited to, the relevant privacy and data protection laws and regulations (the “Privacy Law”), the relevant laws and regulations on the use of human materials, and all relevant guidance relating to clinical studies from time to time in force, including, but not limited to, the ICH Harmonized Tripartite Guideline for Good Clinical Practice (CPMP/ICH/135/95) (“ICH GCP”) and the World Medical Association Declaration of Helsinki entitled “Ethical Principles for Medical Research Involving Human Subjects”. Informed consent was obtained for all patients recruited in the Core Dataset of CENTER-TBI and documented in the e-CRF. Ethical approval was obtained for each recruiting site. The list of sites, Ethical Committees, approval numbers and approval dates can be found on the project’s website https://www.center-tbi.eu/project/ethical-approval (accessed on 15 July 2022).

2.3. Instruments

2.3.1. Quality of Life after Traumatic Brain Injury (QOLIBRI)

The QOLIBRI is the first instrument specifically developed for individuals after TBI to assess their disease-specific HRQoL. It comprises 37 items associated with four scales (Cognition, Self, Daily Life and Autonomy, and Social Relationships) with items measuring satisfaction with various aspects of HRQoL (part A) and two scales (Emotions and Physical Problems) measuring issues that individuals after TBI feel bothered by (part B). Responses to the Part A items are coded on a 5-point Likert scale with 1 corresponding to not at all satisfied and 5 to very satisfied. Responses to the items in Part B are reversely scored to correspond with the items of the Part A. Here, 1 indicates very (bothered) and 5 means not at all bothered. Like other instruments measuring quality of life, when scoring the QOLIBRI scale, means are converted to a 0 to 100 rating scale by subtracting 1 from the mean score and then multiplying it by 25, with a value of 0 indicating the worst possible HRQoL and a value of 100 the best possible HRQoL.
For the general population sample, three items of the original QOLIBRI had to be reworded to remove the reference to a TBI. The fifth item from the scale “Self”, “How satisfied are you with what you have achieved since your brain injury?”, was changed to “How satisfied are you with what you have achieved recently?”. The second item from the scale “Physical”, “How bothered are you by effects of any other injuries you sustained at the same time as your brain injury?”, was changed to “How bothered are you by the effects of any injuries you sustained?”. The last item, also assigned to the scale “Physical”, “Overall, how bothered are you by the effects of your brain injury?”, was changed to “Overall, how bothered are you by the effects of any health problems?”.

2.3.2. Sociodemographic and Health Status Data

The sociodemographic and health status data for both samples contained information on sex, age and the highest level of education achieved. In addition, the presence of chronic health conditions (CHC) was recorded for the general population sample, where multiple answers were possible. The question was: “Do you have any of the following chronic health complaints?” Subjects were asked to tick a box for the response options (multiple answers were possible) listed in Table A1.
Additionally, the Glasgow Coma Scale (GCS) was used in the TBI sample to rate TBI severity [36]. A score of 13 to 15 points indicates mild TBI, 9 to 12 moderate TBI, and 3 to 8 severe TBI. The Glasgow Outcome Scale Extended (GOSE), ranging from 1 (death) to 8 (upper good recovery), was used as a measure of recovery status after TBI [37].

2.4. Participants

2.4.1. General Population Sample

Participants from the general population sample were recruited by a market research agency (Dynata, Shelton, CT, USA) between 29 June and 31 July 2017. To obtain a representative sample, participants were invited until the required quotas for age, sex and level of education had been achieved. Due to the self-reported nature of the data collection, the sex of participants was collected as gender (male, female). Since gender/sex corresponds to the biological categories of males and females, the word “sex” will be used for consistency and to avoid any confusion. Comparison of the quotas with demographic information obtained from the Organization for Economic Cooperation and Development databank (OECD) [38] and Eurostat database [39] revealed a widely comparable distribution of the groups. Within this online survey based on self-report, the data were collected in Italy, the Netherlands, and the UK. The reference values of the QOLIBRI for the Netherlands and the UK have already been published [40].
In order to increase the representativeness of the sample, Dynata deployed a variety of methods to engage people with diverse motivations to take part in research and to reach participants with different socioeconomic statuses. To avoid self-selection bias, specific details of the project were not visible at the time of the invitation. The project details were only disclosed later on. Participants who answered the survey in less than five minutes were automatically excluded from the analysis. Additionally, participants with contradictory response patterns were excluded. For the QOLIBRI, the following answers were excluded as they were contradictory: If someone chose responses at either the left or right extremes of the Likert scale, that meant that they were not satisfied at all, but also not bothered at all. All collected data were anonymized. The nonresponse rate of the survey was 14.1%. Figure 1 shows the general Italian population sample attrition.

2.4.2. TBI Sample

Participants in the TBI sample were a part of the CENTER-TBI study (EC grant 602150), which collected data from 4509 patients in 18 countries [35]. The following inclusion criteria had to be fulfilled: a clinical diagnosis of TBI, presentation in the hospital fewer than 24 h after injury, and an indication for computed tomography (CT). Data were collected between 9 December 2014 and 17 December 2017 via face-to-face visits, in hospital visits, via telephone interviews, or a combination of telephone interview and e-mail. Data on sex, age, time since injury and education was collected at study enrollment based on medical records and self-report. The information on age at study enrollment reflects the age at injury. The QOLIBRI data used was obtained around three months post-injury (i.e., minus two to plus five weeks). Figure 2 shows the TBI sample attrition. No participants with contradictory response patterns were identified. Therefore, all were included in the analyses.

2.5. Statistical Analyses

The following section describes the statistical analyses in detail. All the analyses were carried out using R version 4.0.3 [41] employing the packages lavaan [42] and semTools [43] for the calculation of Confirmatory Factor Analysis (CFA) and MI, respectively. The significance level was set at 5%.

2.5.1. Item and Scale Characteristics of QOLIBRI in General Population

Firstly, the item characteristics of the reworded QOLIBRI were examined. This included means, standard deviations, skewness, and a check of the floor and ceiling effects. Skewness was characterized as symmetric for values from −0.5 to 0.5, moderately skewed from ±0.5 to ±1, and highly skewed for values above ±1 [44]. On the scale level, the internal consistency of items was calculated using Cronbach’s alpha. Then, the correlation between scales and the range of correlations between items and their home scales were checked. In order to evaluate the ceiling effects, a cut-off value of 40% was chosen for the highest category “very”. This is twice as high as the 20% that could be expected by chance with five categories. For the floor effects, we controlled by combining the response categories “not at all” and “slightly”, with a cut-off of 10%. The recommendations of the World Health Organization Quality of Life (WHOQOL) Group [45] were followed to exclude items with a Corrected Item-Total Correlation (CITC) higher than 0.4. However, no items had to be excluded.

2.5.2. Construct Validity of QOLIBRI in General Population

We used confirmatory factor analysis (CFA) to verify whether the six-factor structure of the original questionnaire could be replicated for the adapted QOLIBRI applied in the general reference population sample. For this purpose, we first estimated three models: a one-factor model, a two-factor model, and the original six-factor model. The one-factor model assumed a general factor HRQoL that is associated equally with all 37 QOLIBRI items. The two-factor model assumed two intercorrelated factors, where one factor included items from the QOLIBRI that represented satisfaction with certain aspects of an individual’s life (Part A) and the second factor reflected feeling bothered with some aspects of one’s life (Part B). The six-factor model which was described above in detail comprised six factors (Cognition, Self, Daily Life and Autonomy, Social Relationships, Emotions and Physical Problems). Finally, the models were compared using chi-square difference tests.

2.5.3. Measurement Invariance between Samples

The examination of the MI included analyses of individual responses from both samples. Due to the limited sample size in the TBI sample, we had to dichotomize the response categories of the QOLIBRI, with the response categories “not at all” and “slightly” forming the lower category and the response categories “moderately”, “quite” and “very” the higher category. We therefore followed the approach of Wu and Estabrook [46] when testing MI for dichotomized response categories. We estimated increasingly constrained models and compared the model fit among these. We first estimated the baseline model, which is mostly equivalent to configural MI and freely estimates all four parameters (thresholds, loadings, intercepts and residuals). Here, the requirement of configural MI is satisfied when the same number of factors and the same pattern of loadings are equal for both groups. We then estimated the second model, where three parameters are restricted and the thresholds are freely estimated, which corresponds to partial MI. Finally, in the last model, all four parameters were restricted, which is equivalent to full MI.

2.5.4. Regression Analysis

Research suggests that age [47], gender [48], education [49] and the presence of chronic health conditions (CHC) [50,51] have an impact on HRQoL. Therefore, to generate reference values that represent HRQoL for meaningful subgroups, we investigated the influence of these factors on HRQoL as measured by the QOLIBRI total score using multiple linear regression. Available information from the general population sample on these variables and their interactions was included in the regression model. Age was binned into six ordered age categories (18 to 24; 25 to 34; 35 to 44; 45 to 54; 55 to 64; older than 65 years). Bearing in mind that the age—in the form of 10-year age bins—had a significant influence on the total score of the short form of the QOLIBRI, its overall scale—QOLIBRI-OS, in the Italian population [52], the same age bins were used here. Sex was categorized as female and male. Education was assessed as the highest level of education and categorized as one of the following three: low (primary school), middle (diploma, secondary school, high school, or post-high school), or high (college or university). Participants were categorized in terms of CHCs either being present (when they reported at least one CHC) or being absent. The dependent variable was the participants’ QOLIBRI total score.

2.5.5. Reference Values from the General Population Sample

Based on the results of a linear regression analysis, tables were presented with population reference values in form of percentiles (2.5%, 5%, 16%, 30%, 40%, 50%, 60%, 70%, 85%, 95% and 97.25%). Values below the 16th percentile and above the 85th percentile (both rounded up to the next integer) represent low and excellent HRQoL, respectively. These can be used to evaluate whether an individual’s QOLIBRI total score is below, equal to, or above the value of the respective reference group.

3. Results

The sociodemographic characteristics of the general population sample are presented in Table 1. Both sexes were represented equally. The mean age of this sample was 45.27 (SD = 14.85) years. Slightly more than a half of the participants (53.97%) reported no CHCs. Detailed information on specific CHCs per age group can be found in Appendix A, Table A1.
Sociodemographic and clinical characteristics of the TBI sample are presented in Table 2. The mean age was 50.63 (SD = 20.75) years and 68.8% of the TBI sample were males. Most subjects (55.94%) had an intermediate level of education. The majority of the TBI sample sustained a mild TBI. Over half of the participants (53.73%) recovered well after TBI.

3.1. Item and Scale Characteristics of QOLIBRI in the General Population

Item characteristics including mean value, skewness, and floor and ceiling effects are presented in Table 3. On average, individuals were rather satisfied with their HRQoL (M = 3.62 [3.11–4.02]). The lowest satisfaction scores related to questions on anger or aggression (M = 3.11, SD = 1.26) and the highest satisfaction scores were reported in connection with the ability to find one’s way around (M = 4.02, SD = 0.98), the ability to get out and about (M = 4.02, SD = 1.02), and the ability to carry out domestic activities (M = 4.02, SD = 0.97). With skewness values from 0 to ±0.99, the item distribution can be considered as moderately skewed. None of the satisfaction items from the Part A exceeded the cut-off value for ceiling effects. The reversed scales “Emotions” and “Physical Problems” in Part B, containing bothered items, showed higher values, indicating that individuals from the general population sample were mostly not bothered by problems present in the TBI population. The scales “Cognition” and “Physical Problems” were below the cut-off value of 10%, indicating that the healthy population sample had very few problems in these domains.
Table 4 provides Cronbach’s alpha characterizing the internal consistency of the six QOLILBRI scales. Coefficients ranged from 0.87 to 0.92 indicating good to excellent internal consistency of the QOLIBRI scales [53]. Based on corrected item-total correlations (CITC) and the cut-off of 0.40, all items were considered consistent. The subscales were moderately to highly intercorrelated (r between 0.35 and 0.77). The highest correlation was found between the subscales “Daily Life and Autonomy” and “Self” (r = 0.83), while the lowest correlation was between the scales “Emotions” and “Cognition” (r = 0.35).

3.2. Construct Validity of the QOLIBRI in the General Population

In order to evaluate the latent factor structure of the adapted QOLIBRI, CFAs were carried out, comparing the one, two and six factorial models. Table 5 summarizes the goodness of fit indices for these models, showing the best fit for the six factorial model with χ2(614) = 7473, p < 0.001, CFI = 0.994, and RMSEA = 0.058, 90% CI (0.057; 0.059) [54].

3.3. Measurement Invariance

The results of the MI analyses indicated no significant difference between the configural and partial invariance models (Table 6), thus partial invariance can be assumed. However, a comparison of the partial and full invariance models revealed statistically significant differences, indicating that thresholds differed between these models. Further analysis has been undertaken to assess the practical significance of these differences. Examining the thresholds in the partial invariance model showed that these values differed between the general population sample and the TBI sample (Table A2), indicating that the response behavior was not identical in both groups. However, these threshold differences did not exceed 5%. Therefore, the difference between partial and full measurement invariance can be interpreted as being non-significant, resulting in full measurement invariance between the TBI and general population sample. Thus, when comparing QOLIBRI scores between general population and TBI population samples, the differences in scores can be attributed to real differences in HRQoL.

3.4. Linear Regression Analysis

Regression analysis revealed a significant impact of age, CHCs and education (Table 7). Individuals in all other age groups displayed significantly higher QOLIBRI scores than individuals aged 18 to 24 years. The presence of a CHC significantly influenced HRQoL, since healthy individuals had higher QOLIBRI scores than individuals with at least one chronic health condition. Individuals with a high, but not those with a medium level of education had significantly higher QOLIBRI scores than individuals with lower education. The effect of sex or any other interaction did not significantly contribute to explaining the QOLIBRI scores.

3.5. QOLIBRI Reference Values for the Italian General Population

Based on the results of the regression analysis, reference values were stratified by age, level of education, and the presence of at least one CHC (Table 8). Additionally, we stratified reference values by sex because prior research on HRQoL in individuals after TBI indicates sex effects on HRQoL [55,56,57]. Reference values without categorization by sex can be found in the Appendix A (s. Table A3). Reference tables for the QOLIBRI subscales can be found in Appendix A (s. Table A4, Table A5, Table A6, Table A7, Table A8 and Table A9).
The following example will try to illustrate how to use these values. After a TBI, a 50-year-old woman with diabetes presented with a QOLIBRI total score of 65. The appropriate reference values are those of females with at least one CHC in the age group of 45 to 54 years (Table 8). Table 8 shows that about 65% of individuals in her age group reported the same or a lower level of HRQoL. Her value lies in the range of one standard deviation above the median and can thus be considered as being average. Based on the 16%-percentile cut-off value, HRQoL is interpreted as being below average for female individuals of 50 years with one CHC when the QOLIBRI total score is lower than 42.

4. Discussion

The aim of this study was to provide reference values for the QOLIBRI derived from a general Italian population sample. For that purpose, some conditions had to be fulfilled. First, CFA was used to verify that the adjusted QOLIBRI had the assumed six-factorial structure (Cognition, Self, Daily Life and Autonomy, Social Relationships, Emotions, Physical Problems) like the original QOLIBRI version for adults after TBI. This requirement was met and the results were almost consistent with an earlier study [40] that applied the adapted QOLIBRI questionnaire to general population samples from the Netherlands and the UK.
Gorbunova et al. [40] showed that in the Dutch population, the interaction between gender and CHCs was also significant in the regression analysis. This was not the case in the Italian or in the United Kingdom populations. Concerning the QOLIBRI total score without further stratification, a value below 50 obtained from general Italian sample indicates impaired HRQoL. The values obtained from the English and Dutch general population samples were lower (i.e., 44 for the UK) and higher (i.e., 55 for the Netherlands), respectively [40]. Since no differences can be observed in terms of the distribution of the sociodemographic or health-related factors, these findings can be explained by the differences in HRQoL across the countries [58,59,60,61]. For example, Alonso et al. [61] found that participants from the Netherlands (M = 55.2) reported the highest generic mental HRQoL score as measured using the Short Form-36 (SF-36) mental component summary score, compared with other countries (e.g., Italy: M = 50.3). In addition, the European Study of Epidemiology of Mental Disorders within six countries found that the proportion of respondents reporting problems on any of the EuroQol-5 Dimensions (EQ-5D) [62] was significantly higher in France and lower in Spain and Italy [58]. Taken together, all these differences emphasize the importance of country-specific reference values, which is also the case for TBI-specific HRQoL assessments.
The MI analyses indicated that the same construct was measured in the general Italian reference sample and in the TBI population. Although the full MI model differed from the partial MI model in terms of model fit, analyses of threshold fluctuations indicated that thresholds did not differ more than 5% and were thus negligible. The same conclusion could also be drawn for the QOLIBRI in the Dutch and UK samples [40,58,59,60,61].
Our results showed that younger age, presence of CHCs, and lower level of education are associated with worse HRQoL measured using the QOLIBRI. Wu et al. [52] found similar results for the use of the short version of the QOLIBRI, the QOLIBRI-OS, in an Italian general population sample providing reference values. The use of the same age bins in calculating the regression analyses presented, as well as in stratifying the reference values, ensures that the reference values of the two instruments are comparable in the future. Regarding age differences, a study examining HRQoL after heart failure found that older patients’ HRQoL exceeded expectations for their age, whereas younger individuals complained of loss of activities or roles and rated their HRQoL as being correspondingly worse. The authors suggested that better HRQoL in older compared with younger patients was due to the older patients’ ability to reconceptualize their expectations in relation to their health problems. Duke et al. [63] also demonstrated that older people who had adapted their activities to the chronic illness in question had better mental health, suggesting that it is not just the presence of health problems or young age that determines good quality of life.
In addition, it should be noted that sex did not play a role either in the study by Wu et al. [52] nor in the present study. However, the literature on TBI regarding sex or gender differences is inconsistent [57,64,65,66], while there is strong evidence that gender represents an influential factor in TBI [67]. Previous research shows that sex differences were found to possibly affect sustaining a TBI [68], to impact post-concussion symptoms [56,69], depression [70], anxiety [70], as well as recovery after TBI [71,72]. A recent study by Mikolic et al. (2021), examining differences between men and women in treatment and outcome after TBI, finds that after mild TBI women reported lower generic and disease-specific HRQoL than men. Despite controversial research findings, gender/sex seems to be important for outcome assessment after TBI. Therefore, we have also added a stratification of reference values by sex in addition to the stratification by age, presence of CHC and education.
In contrast to our TBI sample showing a negative association between the HRQoL and age (r = −0.18), as well as to prior research that has found a decrease in HRQoL in older subjects with a TBI history [47], the general population sample investigated in the present study displayed higher HRQoL with increasing age. This is in line with findings from a non-TBI Taiwanese sample, which showed a positive effect of age on mental HRQoL and negative influence on physical HRQoL measured using the generic Short Form 12 (SF-12) [73]. In our sample, we used the QOLIBRI total score, which incorporates both mental and physical aspects of HRQoL. Further research should investigate the differential effects of age on individual QOLIBRI dimensions.
It is reasonable to assume that chronic health problems have an influence on HRQoL [74]. Our results showed that individuals with CHCs exhibited lower QOLIBRI total scores than individuals without CHCs. These results are consistent with previous research which indicates an inverse relationship between CHCs and HRQoL [75].
In addition, level of education was also associated with better HRQoL. Individuals with a higher education level reported higher QOLIBRI total scores in comparison to individuals with low education levels. These findings are in line with prior research showing an association between higher education levels and better HRQoL in non-TBI [76] and TBI [77,78] populations. The relationship between education and HRQoL can likely be explained by the opportunities higher education and better socioeconomic status provide, furthering, for example, self-determination through better income and better access to health services [79,80,81].

4.1. Strengths and Limitations

The most important strength of our study is the number of survey participants, which allowed reference values to be calculated stratified by several sub-groups. For example, we were able to provide reference tables for the individuals with and without CHCs and integrating the education levels. The interpretation of HRQoL for Italian individuals after TBI has thereby been improved. Furthermore, reference values based on percentiles are a common approach in clinical practice, facilitating the interpretation and communication of the QOLIBRI scores. The comparison with a (healthy) general population improves the comprehensibility of the test results for the patients.
This study also has several limitations that may require discussion. The first limitation concerns the recruitment of the general population sample. Recruitment was carried out via online platforms and strived for maximum representativeness. However, the online nature of the recruitment only captures certain population groups, such as only those who have Internet access, which may have led to selection biases [82]. In addition, we do not have information about those who declined the survey invitation, which is one of the main issue of online surveys [83]. Possible carelessness in answering online surveys [84] as well as the lack of opportunity to verify the authenticity of the data are notable limitations [82]. Moreover, the severity of the CHCs, as well as their duration, were not recorded because the analyses of these characteristics were beyond the scope of this study. Future studies may investigate the influence of these factors on disease-specific HRQoL.
With respect to the TBI sample, it should be noted that its relatively small size made a dichotomization of the QOLIBRI’s response categories necessary, which always results in a loss of information [85,86]. Furthermore, the vast majority of the TBI sample (71%) consisted of mild TBI, which could have led to response categories not being exhausted (e.g., not at all satisfied or very bothered), requiring the modification of the number of response categories for MI analysis. However, this limitation only concerns the comparison of the QOLIBRI between the general and the TBI sample. To fill this gap, future research should investigate potential differences between Italian TBI and general population samples employing larger TBI samples. With regard to injury severity in the TBI sample, it should be noted that 13.7% of subjects had missing information, which is common in clinical trials. These missing data were not imputed since this information has not been used in the further analyses. The 13.7% of missing values for education were either due to the fact that the level of education was unknown or not reported. Since we did not include any of the above variables in determining the reference values and used them only for the descriptive statistics of the TBI sample, the missing values had no further impact on our results.
The QOLIBRI is an internationally widely used instrument, which has been translated into 26 languages. The reference values for the Italian population presented here may help to consider cultural differences in HRQoL. In addition to the total score, reference values on the subscale level allow the HRQoL domains to be evaluated more precisely. However, to date, there are reference values only for two further countries (i.e., the Netherlands and the UK). Therefore, further studies are required that investigate country-specific reference values for the QOLIBRI in the general population to enable multinational studies on TBI supporting the understanding of the clinical meaning of HRQoL after TBI.

4.2. Conclusions

This study contributes to TBI outcome research by providing reference values for the TBI-specific instrument QOLIBRI for an Italian general population stratified by age, education, gender, and the presence of CHCs. Researchers and clinicians are now able to employ reference values for individuals from Italy which could help them to better interpret HRQoL after TBI in individuals and to adjust their treatment accordingly, which in turn could help to improve the quality of life of the individuals concerned.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/jcm12020491/s1, Membership of CENTER-TBI Participants and Investigators is provided in the Supplementary Materials.

Author Contributions

Data Collection: the CENTER-TBI Participants and Investigators; Research question and design of the study: N.v.S.; Conceptualization: U.K., S.G., M.Z. and N.v.S.; Data curation: U.K., S.G., S.P. and J.H.; Formal analysis: U.K. and S.G.; Investigation: J.H.; Methodology: U.K., S.G., M.Z. and N.v.S.; Software: U.K. and S.G.; Supervision: N.v.S.; Visualization: U.K.; Writing—original draft: U.K.; review and editing: U.K., S.G., M.Z., J.H., S.P. and N.v.S. All authors have read and agreed to the published version of the manuscript.

Funding

CENTER-TBI was supported by the European Union 7th Framework program (EC grant 602150). Additional funding was obtained from the Hannelore Kohl Stiftung (Bonn, Germany), from OneMind (Napa, CA, USA), from Integra LifeSciences Corporation (Princeton, NJ, USA) and from Neurotrauma Sciences (Alpharetta, GA, USA).

Institutional Review Board Statement

The CENTER-TBI study (EC grant 602150) has been conducted in accordance with all relevant laws of the EU if directly applicable or of direct effect and all relevant laws of the country where the recruiting sites were located, including, but not limited to, the relevant privacy and data protection laws and regulations (the “Privacy Law”), the relevant laws and regulations on the use of human materials, and all relevant guidance relating to clinical studies from time to time in force, including, but not limited to, the ICH Harmonized Tripartite Guideline for Good Clinical Practice (CPMP/ICH/135/95) (“ICH GCP”) and the World Medical Association Declaration of Helsinki entitled “Ethical Principles for Medical Research Involving Human Subjects”. Informed consent was obtained for all patients recruited in the Core Dataset of CENTER-TBI and documented in the e-CRF. Ethical approval was obtained for each recruiting site. The list of sites, Ethical Committees, approval numbers and approval dates can be found on the project’s website https://www.center-tbi.eu/project/ethical-approval (accessed on 15 July 2022).

Data Availability Statement

All relevant data are available upon request from CENTER-TBI, and the authors are not legally allowed to share it publicly. The authors confirm that they received no special access privileges to the data. CENTER-TBI is committed to data sharing and in particular to responsible further use of the data. Hereto, we have a data sharing statement in place: https://www.center-tbi.eu/data/sharing (accessed on 1 July 2022). The CENTER-TBI Management Committee, in collaboration with the General Assembly, established the Data Sharing policy, and Publication and Authorship Guidelines to assure correct and appropriate use of the data as the dataset is hugely complex and requires help of experts from the Data Curation Team or Bio- Statistical Team for correct use. This means that we encourage researchers to contact the CENTER-TBI team for any research plans and the Data Curation Team for any help in appropriate use of the data, including sharing of scripts. Requests for data access can be submitted online: https://www.center-tbi.eu/data (accessed on 1 July 2022). The complete Manual for data access is also available online: https://www.center-tbi.eu/files/SOP-Manual-DAPR-2402020.pdf (accessed on 1 July 2022).

Acknowledgments

The authors would like to cordially thank all patients, study participants and CENTER-TBI investigators.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Table A1. Prevalence of CHC per age group.
Table A1. Prevalence of CHC per age group.
CHC (N)18–24
(n = 310)
25–34
(n = 565)
35–44
(n = 741)
45–54
(n = 664)
55–64
(n = 586)
<65
(n = 432)
Total
(n = 1518)
Asthma264860414126242
Heart Disease27510182062
Stroke565105738
Diabetes132534505257231
Back Complaints123143504328207
Arthritis632496410168320
Rheumatism43043515537220
Cancer561111111862
Memory Problems due to Dementia413131111254
Memory Problems due to Ageing5711254744139
Depression57951111058150499
Other193565898056344
Table A2. Response probabilities estimated for general population sample from the full invariance model in comparison to TBI sample.
Table A2. Response probabilities estimated for general population sample from the full invariance model in comparison to TBI sample.
General Population
(TBI as a Ref.)
COGNITIONThresholds
Concentrate0.704 (0.000)
Expressing yourself0.757 (0.000)
Memory0.670 (0.004)
Plan and problem solving0.753 (0.000)
Decisions0.742 (−0.001)
Navigate0.754 (−0.004)
Speed of thinking0.766 (0.002)
SELF
Energy0.597 (0.009)
Motivation0.628 (0.004)
Self-esteem0.576 (0.003)
Appearance0.518 (0.000)
Achievements0.541 (−0.011)
Self-perception0.580 (−0.001)
Future0.435(−0.004)
DAILY LIFE AND AUTONOMY
Independence0.656 (−0.001)
Get out and about0.745 (0.002)
Domestic activities0.750 (0.002)
Run personal finances0.660 (−0.005)
Participation at work0.662 (0.001)
Social and leisure activities0.546 (0.002)
In charge of life0.628 (−0.002)
SOCIAL RELATIONSHIPS
Affection towards others0.716 (0.000)
Family0.709 (−0.001)
Friends0.649 (−0.002)
Partner0.649 (0.000)
Sex life0.547(0.007)
Attitudes of others0.544 (−0.003)
EMOTIONS
Loneliness0.482 (−0.004)
Boredom0.421 (0.000)
Anxiety0.407 (0.001)
Sadness0.413 (0.002)
Anger/Aggression0.378 (0.000)
PHYSICAL PROBLEMS
Slow/clumsiness0.605 (0.006)
Effects other injuries0.592 (0.011)
Pain0.427 (−0.009)
Seeing/hearing0.534 (−0.005)
Effects health problems0.447 (−0.004)
Note: For measurement invariance testing with TBI samples response categories “not at all” and “slightly” were recorded as 1.
Table A3. Reference values for the QOLIBRI total score obtained from the general population sample in Italy stratified by health status, age, and education.
Table A3. Reference values for the QOLIBRI total score obtained from the general population sample in Italy stratified by health status, age, and education.
Health Status × Age
Low HRQoL−1 SD Md +1 SDHigh HRQoL
Health StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
Healthy18–241993945505661646770799195
25–343463742515762656973829198
35–444434044516065707479849498
45–5433743485562677176808897100
55–6427044485966727477828896100
≥6518552556270747781859299100
At least one CHC18–241112432444851535864728591
25–342191827384850535661728489
35–442982535435155586367758387
45–543272731425155596469788790
55–643162832495660646873798792
≥652473942525963697277839194
Health Status × Education
Low HRQoL−1 SD Md +1 SDHigh HRQoL
Health StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
HealthyLow5913943505864687378859398
Middle102142475562677175798796100
High1684149556467717580869599
At least one CHCLow5203035455256616570788789
Middle8242530445256606570798792
High1743137465156606469798491
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) are within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
Table A4. Reference values for the QOLIBRI Cognition scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table A4. Reference values for the QOLIBRI Cognition scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–2482434750657275818593100100
25–34159253254657275798393100100
35–44201364354687275798697100100
45–54167445065727575798697100100
55–64136435061727575798693100100
≥65894450687576869093100100100
At least one CHC18–24632936505861656875839399
25–3412522294350586872758696100
35–4416118254358657275799097100
45–54173343654657175758393100100
55–64169404161687275798393100100
≥65124405065757577838695100100
MaleHealthy18–2411736505465727575838897100
25–34187364350687275758390100100
35–44242435056727575838697100100
45–54170435065757575798697100100
55–641345061727579849093100100100
≥65966365727579838690100100100
At least one CHC18–244826295061687583869096100
25–34941624405050586572839397
35–4413725325061687275759097100
45–54154242949586872758393100100
55–64147304459687375758390100100
≥65123405065727579838696100100
Sex × Health Status × Education Low HRQoL−1 SD MD +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow321404350657275758393100100
Middle445435061727575838697100100
High68244871757983869097100100
At least one CHCLow296293650616872758390100100
Middle439253350656872758390100100
High80505061727575798693100100
MaleHealthyLow270364354687475798393100100
Middle576455065757579838697100100
High100455061727575798697100100
At least one CHCLow224283650656875758390100100
Middle385233350657275758390100100
High9423284754586875839097100
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
Table A5. Reference values for the QOLIBRI Self scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table A5. Reference values for the QOLIBRI Self scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–2482222540505865717579100100
25–3415981436505865727587100100
35–44201182540546168757586100100
45–54167252950646872757990100100
55–641361831505865727575859797
≥6589414558687275758393100100
At least one CHC18–2463811223643505561657579
25–34125811224047505861758296
35–4416188294350546168758690
45–54173511254350586168759096
55–641691115365055656872759096
≥6512415254050546168727990100
MaleHealthy18–2411725355057656875758695100
25–3418725295054616872758399100
35–44242223650586872757586100100
45–54170233650586572757586100100
55–64134364654657272757990100100
≥6596365362687275757989100100
At least one CHC18–244811253850536168727994100
25–3494611253947505358758697
35–441371122364754586572788390
45–541541118294750586569799093
55–641471521435461657275799095
≥651232226506065687275839393
Sex × Health Status × Education Low HRQoL−1 SD MD +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow321112540546168757586100100
Middle445222947586568757586100100
High68283654656875757990100100
At least one CHCLow296815294750546568758696
Middle439811294350586168759097
High801522365056586568798386
MaleHealthyLow270253347546568757586100100
Middle576273650616872757586100100
High100252950646872757586100100
At least one CHCLow2241725405058656872779098
Middle3851122344754616572798993
High94614324350546568799396
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
Table A6. Reference values for the QOLIBRI Daily Life and Autonomy scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table A6. Reference values for the QOLIBRI Daily Life and Autonomy scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD MD +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–2482334350546568727586100100
25–34159253348586872758393100100
35–44201364050617275798697100100
45–541674048586873758386100100100
55–64136384056687575838693100100
≥65894852687579869093100100100
At least one CHC18–24631218405050586168829395
25–341258163347546170758497100
35–4416115224050616875758697100
45–5417312254354616872798698100
55–6416912275061687275798697100
≥65124364050616872798393100100
MaleHealthy18–2411733395058657275798697100
25–34187334150616872757990100100
35–44242254350687275758393100100
45–54170414761727575838693100100
55–64134505365757579869097100100
≥6596586575757983869097100100
At least one CHC18–244819244351546875759097100
25–34941122364750545865768796
35–441372528405063687275859797
45–5415421254354616872758697100
55–64147173450656875757990100100
≥65123253354687275798392100100
Sex × Health Status × Education Low HRQoL−1 SD MD +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow321334050616875758393100100
Middle445334054667475839097100100
High68404563727583839097100100
At least one CHCLow29611184050586872758697100
Middle43915224354616875799097100
High80183650586872798390100100
MaleHealthyLow270344150617175758393100100
Middle576405058687575798393100100
High100344758717575758693100100
At least one CHCLow2242233475465687575869698
Middle38518254354656875758697100
High94253140505865687590100100
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
Table A7. Reference values for the QOLIBRI Social Relationships scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table A7. Reference values for the QOLIBRI Social Relationships scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–2482213850606771757588100100
25–34159212550607175758096100100
35–44201303050636775758096100100
45–54167304255637175808497100100
55–64136303353677175758088100100
≥6589424655717575808892100100
At least one CHC18–24631521384650556371789596
25–34125914385055636775849596
35–4416113214255636771758896100
45–541739173450596771758898100
55–6416918254255596775788896100
≥6512426344659647175808896100
MaleHealthy18–2411721305055636775758497100
25–3418720254659637175758496100
35–44242263850596775758092100100
45–54170253050637175758192100100
55–64134273756677575808496100100
≥6596384863717575758492100100
At least one CHC18–244814243846555965808896100
25–34941313334247505867759295
35–44137516375459677175808996
45–541549133646556571758496100
55–6414725305059677175758896100
≥651232234506367717584919696
Sex × Health Status × Education Low HRQoL−1 SD MD +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow321213050637175758496100100
Middle445263450637175758096100100
High68344259676775808396100100
At least one CHCLow29613174253596771758896100
Middle4399173850596771758896100
High802538465559657175809292
MaleHealthyLow270253050597175758492100100
Middle576253450636775758088100100
High100173454636775757584100100
At least one CHCLow22413254555637175768896100
Middle3851114385059677175859696
High9414213750515966758898100
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
Table A8. Reference values for the QOLIBRI Emotions scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table A8. Reference values for the QOLIBRI Emotions scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–24826102535425050607595100
25–3415951025354550556885100100
35–44201152030405050607585100100
45–54167101530405060708095100100
55–64136252535505565758595100100
≥65892025405060758090100100100
At least one CHC18–246300152330353645548095
25–3412502202530354550658590
35–44161052030354550607590100
45–54173052534404555658195100
55–641691010253545506070859599
≥65124151630455565748090100100
MaleHealthy18–2411710102535454550607895100
25–34187101530404550606685100100
35–44242202530455060707590100100
45–54170202535455060708090100100
55–641341725355065707990100100100
≥6596223042637078808595100100
At least one CHC18–24481010253035405055608490
25–3494010253540505055658499
35–4413781525354550536075100100
45–54154101525354550556585100100
55–6414717253545506065758195100
≥65123202140505565728090100100
Sex × Health Status × Education Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow321151530405050657590100100
Middle445101530405055657590100100
High68121533455060718095100100
At least one CHCLow296002030404550658095100
Middle4395102530404555658095100
High801015253544505565808596
MaleHealthyLow270141835505060707595100100
Middle576152030455060708090100100
High100102030404550677290100100
At least one CHCLow224101630405050607083100100
Middle38510152540455055658095100
High94514304040505560759094
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
Table A9. Reference values for the QOLIBRI Physical Problems scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table A9. Reference values for the QOLIBRI Physical Problems scale obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–2482202645505265707590100100
25–341591530455060657580100100100
35–44201252545506070758595100100
45–541672525455565708085100100100
55–64136222940586575808590100100
≥65891427506775859095100100100
At least one CHC18–24631825304550556170809598
25–341255152540505060708094100
35–441611020304045506065809095
45–541735103040455062708098100
55–64169510254045505565809099
≥651242025344552606980859095
MaleHealthy18–2411715254050556570758895100
25–341872530405055657585100100100
35–442422530455560707585100100100
45–541702530455965708090100100100
55–641343040527075808090100100100
≥65962430527375808590100100100
At least one CHC18–24483030404655657075809495
25–3494202440505060657580100100
35–44137202535505055607085100100
45–5415410153545505565708092100
55–641471920354550606570809095
≥651231620405055606575859095
Sex × Health Status × Education Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow321202540506065758090100100
Middle4451525455565758085100100100
High682535456070738085100100100
At least one CHCLow2965103040505060708095100
Middle43910153040455060708095100
High801020354450606570808691
MaleHealthyLow270142545506070758095100100
Middle5762530455565758085100100100
High100303550556575758096100100
At least one CHCLow22410203550505565708595100
Middle38515203545506065758090100
High942525404550556070859595
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.

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Figure 1. General population sample attrition chart.
Figure 1. General population sample attrition chart.
Jcm 12 00491 g001
Figure 2. TBI sample attrition chart.
Figure 2. TBI sample attrition chart.
Jcm 12 00491 g002
Table 1. Characteristics of the general population sample (N = 3298).
Table 1. Characteristics of the general population sample (N = 3298).
Age (years)MeanSDRange
45.2714.8557
GroupN%
SexMale164950
Female164950
Education
level
Low111133.69
Middle184555.94
High34210.37
Number of
chronic health complaints
None178053.98
One94828.74
Two and more57017.28
Note: N = number of cases, % = relative frequencies, SD = Standard deviation, low = primary school; middle = diploma, secondary school, high school, or post-high school; high = college or university.
Table 2. Characteristics of the TBI sample (N = 256).
Table 2. Characteristics of the TBI sample (N = 256).
Age (years)MeanSDRange
50.6320.7575
GroupN%
SexMale17668.8
Female8031.2
Education
level
Low41.6
Middle16664.8
High5119.9
Missing3513.7
Mild18271.1
TBI severity (GCS) Moderate2710.5
Severe4718.4
Missing3513.7
Recovery status (GOSE) at 3 months post injury Good recovery (7–8)13553.7
Moderate disability (5–6)5220.3
Severe disability (2/3–4)6927.0
Note: N = number of cases, % = relative frequencies, SD = Standard deviation, GCS = Glasgow Coma Scale, GOSE = Glasgow Outcome Scale Extended.
Table 3. Item characteristics of the QOLIBRI in the general population.
Table 3. Item characteristics of the QOLIBRI in the general population.
MeanSDSkewness% in Cat. “Very”% in Cat. “Not at All” and “Slightly”
Cognition
Concentrate3.830.93−0.7923.48.2
Expressing yourself3.970.91−0.8729.66.9
Memory3.780.92−0.6321.38.7
Plan and problem solving3.950.91−0.8728.67.2
Decisions3.960.94−0.8730.97.1
Navigate4.020.98−0.9936.37.7
Speed of thinking4.000.87−0.8330.45.4
Self
Energy3.590.95−0.6314.512.1
Motivation3.660.99−0.6718.812.0
Self-esteem3.531.08−0.6018.116.6
Appearance3.381.07−0.5412.119.1
Achievements3.461.05−0.5714.316.6
Self-perception3.521.04−0.6315.215.9
Future3.171.14−0.3910.025.0
Daily Life and Autonomy
Independence3.791.10−0.7630.112.5
Get out and about4.021.02−0.9838.79.0
Domestic activities4.020.97−0.9236.27.4
Run personal finances3.771.04−0.7826.011.0
Participation at work3.761.00−0.7423.610.7
Social and leisure activities3.471.09−0.5117.118.5
In charge of life3.671.04−0.6921.612.9
Social Relationships
Affection towards others3.920.99−0.8731.08.0
Family3.861.01−0.8928.49.8
Friends3.691.03−0.7521.312.8
Partner3.711.20−0.8229.915.6
Sex life3.391.27−0.5420.123.0
Attitudes of others3.451.04−0.5813.116.9
Emotions
Loneliness3.481.24−0.246.148.2
Boredom3.221.25−0.068.742.1
Anxiety3.141.34−0.0313.140.7
Sadness3.141.38−0.0414.341.3
Anger/Aggression3.111.260.0011.237.8
Physical Problems
Slow/clumsiness3.801.24−0.624.960.5
Effects other injuries3.721.15−0.513.759.2
Pain3.211.22−0.149.242.7
Seeing/hearing3.541.24−0.376.153.4
Effects health problems3.301.20−0.218.244.7
Table 4. Psychometric properties of the QOLIBRI scales in general population.
Table 4. Psychometric properties of the QOLIBRI scales in general population.
Cronbach’s AlphaItem-Total Correlation RangeCorrelations between Subscales Scores
QOLIBRI Domains (1)(2)(3)(4)(5)
(1) Cognition0.910.67–0.811
(2) Self0.920.69–0.890.691
(3) Daily Life and Autonomy0.900.68–0.800.770.831
(4) Social Relationships0.880.71–0.790.640.760.761
(5) Emotions0.870.62–0.870.350.420.380.391
(6) Physical Problems0.880.66–0.830.380.430.420.310.55
Table 5. Results of confirmatory factor analyses of the QOLIBRI in general population.
Table 5. Results of confirmatory factor analyses of the QOLIBRI in general population.
Model Comparison
ModelCFIRMSEA (90% CI)χ2 (df)pComparison between Models∆χ2 (∆df)p
One-factor0.9320.187 (0.186; 0.188)73,414 (629)<0.001
Two-factor0.9720.120 (0.119; 0.122)30,633 (628)<0.001One- vs. Two-factor3009.9 (1)<0.001
Six-factor0.9940.058 (0.057; 0.059)7473 (614)<0.001Two- vs. Six-factor3496.9 (14)<0.001
Note: CFI: scaled Comparative Fit Index (Cut-off: CFI > 0.95); RMSEA (90% CI, Value for adequate/regular model fit: 0.05 < RMSEA < 0.08): scaled root mean square error of approximation with 90% confidence interval; χ2: scaled chi-square statistics; df: scaled degrees of freedom; p: p-value of chi-square (difference) statistics; ∆χ2: difference in chi-square statistics under Sattora–Bentler (2001) correction; ∆df: difference in degrees of freedom.
Table 6. Results of Measurement Invariance testing: Model comparison.
Table 6. Results of Measurement Invariance testing: Model comparison.
Model Comparison
ModelCFIRMSEA (90% CI)χ2 (df)pComparison between (Invariance Models)∆χ2 (∆df)p
Configural0.9860.030 (0.028; 0.031)3151.63 (1228)<0.001
Partial0.9880.026 (0.025; 0.028)2795.62 (1253)<0.001configural vs. partial7.94 (25)0.999
Full0.9880.027 (0.025; 0.028)2918.75 (1290)<0.001partial vs. full92.95 (37)<0.001
Note: CFI: scaled Comparative Fit Index (Cut-off: CFI > 0.95); RMSEA (90% CI, Value for adequate/regular model fit: 0.05 < RMSEA < 0.08): scaled root mean square error of approximation with 90% confidence interval; χ2: scaled chi-square statistics; df: scaled degrees of freedom; p: p-value of chi-square (difference) statistics; ∆χ2: difference in chi-square statistics under Sattora–Bentler (2001) Correction; ∆df: difference in degrees of freedom; Identification constraints for the invariance models: Configural: item intercepts = 0, residual variances = 1, latent factor means = 0, latent factor variances = 1; Partial: item intercepts = 0, residual variances = 1. Only in the reference group latent factor means = 0 and variances = 1; Full: item intercepts = 0, residual variances = 1. Only in the reference group factor means = 0, factor variances = 1.
Table 7. Results of the linear regression analysis.
Table 7. Results of the linear regression analysis.
Predictors and InteractionsReference GroupβSE
Intercept 63.30 *1.21
Age (25–34)Age (18–24)1.581.38
Age (35–44) 4.64 *1.32
Age (45–54) 7.16 *1.39
Age (55–64) 9.22 *1.45
Age (≥65) 12.53 *1.58
Sex (female)Sex (male)−1.040.74
CHC (yes)CHC (no)−7.66 *1.91
Education (middle)Education (low)1.160.59
Education (high) 1.98 *0.97
Sex (female) × CHCs (yes)Sex (male) × CHCs (yes)−0.561.08
Age (25–34) × CHCs (yes)Age (18–24) × CHCs (yes)−3.512.27
Age (35–44) × CHCs (yes) −2.122.17
Age (45–54) × CHCs (yes) −3.442.19
Age (55–64) × CHCs (yes) −1.912.24
Age (≥65) × CHCs (yes) −1.372.37
Note: β indicates an unstandardized regression coefficient (slope); SE, standard error; CHC, Chronic Health Condition; * Significant at p < 0.05.
Table 8. Reference values for the QOLIBRI total score obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Table 8. Reference values for the QOLIBRI total score obtained from the general population sample in Italy stratified by sex, health status, age, and education.
Sex × Health Status × Age Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusAgeN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthy18–24823843505761636669789496
25–34
35–44
45–54
55–64
159
201
167
136
32
39
42
43
40
43
47
46
51
50
54
55
57
59
64
64
62
64
68
68
66
68
71
73
70
74
76
76
74
79
79
79
82
84
88
86
92
93
98
93
99
95
100
95
≥658949525868737682889399100
At least one CHC18–24632227414648515558708086
25–34
35–44
45–54
55–64
125
161
173
169
18
25
28
28
25
31
32
31
37
42
42
47
49
50
51
56
51
54
55
59
54
57
59
61
58
62
63
65
62
66
69
71
73
76
78
78
85
82
87
87
88
85
90
93
≥651243841505862687277839197
MaleHealthy18–241174446505560656771798894
25–34
35–44
45–54
55–64
187
242
170
134
40
41
44
50
44
45
48
53
51
52
56
63
58
61
62
68
61
67
67
72
65
71
71
75
68
74
75
79
72
79
80
83
82
84
87
91
89
95
96
98
96
98
99
100
≥659656586572747779838999100
At least one CHC18–24483037475154606367778793
25–34
35–44
45–54
55–64
94
137
154
147
22
28
25
29
33
36
29
41
42
45
45
49
48
52
51
58
50
56
55
62
52
60
59
66
55
64
65
71
60
68
69
75
69
75
78
80
81
84
88
86
87
90
90
89
≥651234143566166697377839192
Sex × Health Status × Education Low HRQoL−1 SD Md +1 SDHigh HRQoL
SexHealth StatusEducationN2.5%5%16%30%40%50%60%70%85%95%97.25%
FemaleHealthyLow32139435058636772778494100
Middle4453945536165717579889599
High684351596570747982879295
At least one CHCLow2962832424954586368788689
Middle4392428435255596369798794
High803839485557626572788485
MaleHealthyLow2703945515965697379869396
Middle57644495563677175798696100
High1004348556165687478859799
At least one CHCLow2243339495560636771788790
Middle3852734465257616770798792
High941636445053576367798592
Total32983238505661667075839297
Note: HRQoL: Health-Related Quality of Life; 50% percentiles represent 50% of the distribution corresponding to the median (Md); SD: Standard Deviation; values from −1 standard deviation (16%) to +1 standard deviation (85%) are within the regular range (i.e., not impaired HRQoL). Values below 16% denote low HRQoL and values above 85% indicate outstanding HRQoL.
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MDPI and ACS Style

Krenz, U.; Greving, S.; Zeldovich, M.; Haagsma, J.; Polinder, S.; von Steinbüchel, N.; on behalf of the CENTER-TBI Participants and Investigators. Reference Values of the Quality of Life after Brain Injury (QOLIBRI) from a General Population Sample in Italy. J. Clin. Med. 2023, 12, 491. https://doi.org/10.3390/jcm12020491

AMA Style

Krenz U, Greving S, Zeldovich M, Haagsma J, Polinder S, von Steinbüchel N, on behalf of the CENTER-TBI Participants and Investigators. Reference Values of the Quality of Life after Brain Injury (QOLIBRI) from a General Population Sample in Italy. Journal of Clinical Medicine. 2023; 12(2):491. https://doi.org/10.3390/jcm12020491

Chicago/Turabian Style

Krenz, Ugne, Sven Greving, Marina Zeldovich, Juanita Haagsma, Suzanne Polinder, Nicole von Steinbüchel, and on behalf of the CENTER-TBI Participants and Investigators. 2023. "Reference Values of the Quality of Life after Brain Injury (QOLIBRI) from a General Population Sample in Italy" Journal of Clinical Medicine 12, no. 2: 491. https://doi.org/10.3390/jcm12020491

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