Sleep Quality, but Not Personality Traits, Mediates the Relationship between Chronotype and Life Satisfaction: A Study in Young Adults

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

thank you for your manuscript. I have some concerns about different aspects.

First, you did not include all cited references in the reference list.

Second, you argue that conscientiousness is the strongest predictor for morningness preferences. Please clarify what you assume to contribute to the emergence of chronotype. Is chronotype a biological construct or something that develops over the individual development? And what relationship do you assume between personality and chronotype? If you assume a causal relationship, what is causual for what?

Third, it is unclear if you correlated the raw data of the MEQ with the other variables or if you used the three chronotypes for the correlation.

Fourth, you argue that the length of the personality questionnaire could be responsible for the difference in results to other studies. Nevertheless, you argued in the introduction that there are incongruent results for the correlation between personality and chronotype. If this is the case why should it now rely on the length of the questionnaire. Then it follows that the incongruent results in the literature should be due to questionnaire lenght also. Thus, please report the questionnaires (and their length) used in these incongruent results.

Fivth, there are some issues with tables and figures. Figure 1 is missing. It would be more informative to report the descriptive data for the three chronotypes as compared to the grand means.

I also marked some spelling mistakes.

Best regards

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Author Response

First, you did not include all cited references in the reference list.

We reviewed the references and verified that all appear now in the reference list.

Second, you argue that conscientiousness is the strongest predictor for morningness preferences. Please clarify what you assume to contribute to the emergence of chronotype. Is chronotype a biological construct or something that develops over the individual development? And what relationship do you assume between personality and chronotype? If you assume a causal relationship, what is causual for what?

In the introduction we indicate previous findings regarding the association between morningness and conscientiousness. This association was found by many others. We do not imply causative relationship between the two. However, based on these previous studies, we suggested that similar findings will be demonstrated in the current study and that personality factors may mediate relationship between chronotypes and life satisfaction. However, the results of the study did not show such mediation and therefore we did not add any further discussion on the issue. To reduce some possible confusion, we deleted the sentence in the introduction that suggests prediction (line 62) and we replaced the word “explain” by the more accurate term “mediated” in the hypotheses (line 77).

Third, it is unclear if you correlated the raw data of the MEQ with the other variables or if you used the three chronotypes for the correlation.

The initial analyses were performed using the raw MEQ scores as indicated in Table 1 and Table 2. We now further emphasize this by adding “MEQ score” to the text (line 160) and to Table 2. We did use the chronotype groups as well in additional ANOVA analyses as described later in the results section in lines 198-200.

Fourth, you argue that the length of the personality questionnaire could be responsible for the difference in results to other studies. Nevertheless, you argued in the introduction that there are incongruent results for the correlation between personality and chronotype. If this is the case why should it now rely on the length of the questionnaire. Then it follows that the incongruent results in the literature should be due to questionnaire lenght also. Thus, please report the questionnaires (and their length) used in these incongruent results.

Indeed this is an important question but we did not find previous studies using the short questionnaire to examine relationship between personality factors and life satisfaction. To clarify this issue we added some test to the discussion. This text reads: “to the best of our knowledge, the 10-item questionnaire was not previously used in the context of the association between personality traits and life satisfaction” (lines 286-287).

Fivth, there are some issues with tables and figures. Figure 1 is missing. It would be more informative to report the descriptive data for the three chronotypes as compared to the grand means.

Unfortunately, there was some technical issue with the web site during submission. This is now corrected.

I also marked some spelling mistakes.

Thank you for your detailed review, we now corrected all the typos you indicated.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the current study, Lan et al. investigated the relationship between chronotype and life satisfaction among college students, exploring whether sleep quality or Big Five personality traits mediate this association. It was hypothesized that morning types (MT) would report better sleep quality and higher life satisfaction compared to evening types (ET), and that sleep quality would mediate the link between chronotype and life satisfaction. The authors suggest that ET individuals had poorer sleep quality and lower life satisfaction compared to MT individuals. Additionally, chronotype was related to the personality traits of agreeableness and conscientiousness, with MT showing higher scores in both traits. The authors should consider the following points to revise their manuscript:

 

1.     They should include more background on why the specific variables were chosen and how chronotype is linked with these factors would enhance the reader's conceptual understanding.

2.     Consider mentioning the inclusion/exclusion criteria for participants.

3.     One major limitation of the study is that it is heavily skewed towards female participants (210 women vs. 44 men); this should be acknowledged with other limitations in the manuscript, in terms of the generalizing the findings.

4.     More demographic details should be included for better understanding of the sample.

5.     There is a caption for Figure 1 (Mediation analysis depicting the relationship between chronotype and life satisfaction mediated by sleep quality). However, there is no such figure in the manuscript. Please check.

6.     It would be helpful to clearly specify the nature of the correlation in results (e.g., positive or negative).

7.     Please explain the sequence of questionnaires and whether measures were taken to reduce potential biases. For example: did they randomize the questionnaires.

8.     What specific aspects were considered for determining life satisfaction.

 

Comments on the Quality of English Language

English is fine.

Author Response

1. They should include more background on why the specific variables were chosen and how chronotype is linked with these factors would enhance the reader's conceptual understanding.

Amongst many associations between chronotypes and various factors related to well-being, we were interested in some specific aspects, specifically the mediating roles of personality traits and sleep quality. As explained in the introduction, to the best of our knowledge these interactions were not studies previously. By no means we suggest that these are the most important factors or the only ones, but we selected them as they align with our interest in chronotypes and well being and our work on different domains related to circadian rhythms and well-being. We suggest that we explain this point in the introduction. We believe that additional information on other factors that might be involved is beyond the scope of this work and may be more appropriate for a much longer and more detailed review paper.

2. Consider mentioning the inclusion/exclusion criteria for participants.

There were no specific exclusion or inclusion criteria. We now clarify this in the methods section stating “There were no specific inclusion or exclusion criteria and the entire cohort of volunteers was evaluated” (lines 86-87).

3. One major limitation of the study is that it is heavily skewed towards female participants (210 women vs. 44 men); this should be acknowledged with other limitations in the manuscript, in terms of the generalizing the findings.

Thank you for this important comment. We added a short discussion on the issue stating “One major limitation of the current study is that it is heavily skewed towards women. Whereas we did not find differences between men and women in life satisfaction, sleep quality or personality traits (data not shown), the unequal sample certainly casts some doubt on the generalizability of the results” (lines 292-295).

4. More demographic details should be included for better understanding of the sample.

We added a new table (Table 1) with demographic data..

5. There is a caption for Figure 1 (Mediation analysis depicting the relationship between chronotype and life satisfaction mediated by sleep quality). However, there is no such figure in the manuscript. Please check.

Unfortunately, there was some technical issue with the web site during submission. This is now corrected.

6. It would be helpful to clearly specify the nature of the correlation in results (e.g., positive or negative).

We added the nature of each correlation to the relevant results section (lines165-171). The nature of each correlation is also indicated in Table 3 (new Table 3).

7. Please explain the sequence of questionnaires and whether measures were taken to reduce potential biases. For example: did they randomize the questionnaires.

For technical reasons, questionnaires were all administered in the same order. This is not uncommon in the relevant literature.

8. What specific aspects were considered for determining life satisfaction.

As explained in the methods (life satisfaction and quality of life (QoL) uniscale section), life satisfaction was evaluated by a single question using a numerical rating scale spanning from 0-100. This assessment tool was found to have well-established validity.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The Authors explore the intricate relationships among chronotype, personality, sleep quality, and subjective well-being. Based on extensive literature review, the Authors assume a positive correlation between morningness and life satisfaction, with sleep quality and personality traits playing a mediating role in this relationship. In a survey conducted on 254 young adults (with a sizable female preponderance) some weak but significant correlations were found. The most important finding in this study was that sleep quality turned out to be a mediator between chronotype and life satisfaction, with this relationship disappearing in good sleepers.

Remarks:

Line 158 – Table 1.

Typo in line re. Extraversion

Line 168 – Table 2.

Typo in line re. Openness: r=0.59, - ??

Line 224 – Table 4.

Instead/Apart of frequencies, percentages or Chi test would be more informative.

Lines 304-307

Here the intervention is directed  towards evening types. Why not adapt work schedules to accommodate their sleep preferences? Maybe it is worth to be discussed?

Lines 347-349

Reference doubled.  

Lines 386-389

Doubled reference.  

 

Author Response

Line 158 – Table 1.

Typo in line re. Extraversion
We corrected the typo.

 

Line 168 – Table 2.

Typo in line re. Openness: r=0.59, - ??

This typo was corrected, thank you.

 

Line 224 – Table 4.

Instead/Apart of frequencies, percentages or Chi test would be more informative.

 

We added percentages to the table.

 

Lines 304-307

Here the intervention is directed  towards evening types. Why not adapt work schedules to accommodate their sleep preferences? Maybe it is worth to be discussed?

 

We added a reference to this point in the discussion stating “Alternatively, higher awareness to the challenges of individuals with evening chronotypes may influence higher education institutes and employers to develop more flexible schedules” (lines 322-324).

 

Lines 347-349

Reference doubled.  

Lines 386-389

Doubled reference.  

Thank you for your review, it is now corrected.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

thank you for your revised version. I think the manuscript has improved quite a bit. I have just one further question. In table 5 you state a percentage for the morningsness types of the male participants. Why only for this one data point?

Best regards

Author Response

Comment: In table 5 you state a percentage for the morningsness types of the male participants. Why only for this one data point?

Response: We would like to thank the reviewer for the detailed observation; we added percentages to all chronotypes in table 5.    

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript is much improved.  

Author Response

We would like to thank the reviewer.