Decent Work as Determinant of Work Engagement on Dependent Self-Employed

: This article analyzes with a holistic and systematic approach the state of working conditions in self-dependent workers, as well as their e ﬀ ects on workers’ work engagement. For this, a distinction was made between the self-employed, non-dependent self-employed, and wage earners. The sample integrated 42,963 workers who were surveyed, of which 0.03% were dependent self-employed, 13.73% were non-dependent self-employed, and 82.32% were wage earners. The results have broadly conﬁrmed the research purposes and they established that ensuring work engagement is the key to sustainability, growth, and success for workers.


Introduction
One of the main objectives of the International Labor Organization (ILO) since 1999 is to promote decent work. In its origins, decent work was described in terms of "opportunities for both women and men to have decent and productive work in conditions of freedom and equity, security, and human dignity" [1]. The ILO states that decent work makes both an important contribution to sustainable development and becomes an important goal in itself since it is considered a fundamental human right [2]. Currently, decent work is a priority for policy-makers and for society as a whole as a result of globalization processes and the economic recession of the last decade, which have produced dramatic changes in the labor market structure in Europe, generating an increase in unemployment, underemployment, precarious work, and labor inequality.
The new global economies are characterized by complex systems which are highly dynamic and hypercompetitive, causing in some cases, the abuse in the use of resources (also human resources) by companies. This circumstance, together with the development of social awareness regarding human rights and the protection of the environment, has led to a growing interest in sustainability [3]. This is manifested in the proliferation of academic studies on sustainability in different fields of knowledge, such as economy (e.g., [4,5]), management (e.g., [6,7]), sociology (e.g., [8,9]), etc. International organizations such as the United Nations (UN) show also an increasing concern for sustainability. In particular, the UN has established a framework for sustainable development based on 17 objectives (the Sustainable Development Goals), from which two are directly connected to working conditions: the commitment to decent work (Goal 8), and the promotion of health and well-being (Goal 3) [10].
Nowadays, sustainable development is understood in a broad way so that it does not focus solely on environmental protection but also encompasses socio-economic factors that contribute to improving the life quality of the society [11,12]. The quality of life is determined by a compendium of personal and contextual circumstances among which decent work becomes especially relevant. From a sustainable development approach, decent work refers to those working conditions that respect the fundamental rights of workers in terms of health and safety, remuneration, physical and mental integrity, personal development and social integration, empowerment, equal opportunities, etc. [13].
The deterioration of labor market conditions in Europe in recent years becomes a matter of serious concern. The process of outsourcing and flexibilization have generated a new labor market structure [14]. The austerity measures implemented during the economic recession have led to a deep segmentation of the labor market, with significant differences across occupational categories [15]. In particular, these measures have favored the increase in dependent self-employment. The concept of dependent self-employment refers to the employment relationship where workers are formally classified as self-employed but have some characteristics of employees, such as their dependence on a single client, their lack of autonomy to hire personnel and/or or make strategic decisions, etc. [16][17][18]. This occupational category has caught the attention of academics and policy-makers in recent years. This is because some companies are currently falsely classifying such employees as self-employed to circumvent collective agreements and labor regulations regarding the minimum wage, working time legislation, and protection in case of redundancy to reduce its obligations regarding the payment of labor taxes, etc. [19].
Changes in labor market structure-non-standard work contracts, lack of protection, flexible employment, greater insecurity, etc.-becomes a serious threat to both the psychological and physical well-being of workers [20]. Furthermore, not only the employee's well-being is affected by the precariousness of employment, but also their level of work engagement and performance, which subsequently has a negative effect on business results [21,22]. The new occupational categories that have proliferated as a result of globalization and the recession present precarious working conditions, which subsequently undermines work engagement. The number of dependent self-employed has grown rapidly in Europe in recent years, increasing their representation in the labor market from 2% in 2010 to 3.9% in 2015-going from 803 million to 1693 million [18]. Hence, the precariousness of working conditions in Europe, in general, and in certain occupational categories (such as the dependent self-employed) in particular, highlights the importance of analyzing how precariousness affects work engagement [23].
This research assumes that decent work refers to a high quality of work, and on the contrary, poor working conditions lead to indecent work. It is important to note that the concept of decent work is a relative concept since it is determined by the individual´s own vision on her/his own working conditions, which include aspects such as having a living wage, working hours that allow work-life balance, stability, and long-term perspectives, etc. Given the relativity of the concept, it can be very useful to develop a comparative study between different occupational categories, especially considering that studies that analyze dependent self-employed and their levels of work engagement in a systematic way are rare. The scarcity of empirical research on dependent self-employed is motivated by the lack of consensus on its definition and the opacity that characterizes this occupational category. This problem is increased by the difficulties in obtaining reliable and impartial inform on dependent self-employed [24].
This study aims to contribute to the literature in this regard. Specifically, the research has two main objectives. First, to comparatively analyze in a systematic and holistic way the working conditions of dependent self-employed with respect to non-dependent self-employed and wage earners. This analysis will be developed using the European Working Condition Survey (EWCS). The EWCS facilitates the adoption of a holistic approach in the analysis of decent work since it considers the different dimensions of the quality of work that are determinant of decent work: physical environment, work intensity, working time quality, social environment, skills and discretion, prospects, and earnings. Second, to analyze the influence of decent working conditions on the level of work engagement of each of the previous occupational categories. This study proposes that the working conditions of dependent self-employed are more precarious than those of non-dependent self-employed and wage earners, and that subsequently, the levels of work engagement of dependent self-employed are also comparatively lower. Since previous studies generally address this question in a partial or fragmented manner, identifying some isolated working conditions that are undoubtedly of interest but do not provide a comprehensive approach to decent work and its relation with work engagement, the adoption of a holistic approach covers an important research gap (e.g., [25][26][27][28]).

Sustainability, Decent Job, and Work Engagement
The concept of sustainability has been extended since the publication of the Brundtland report (1987) by the UN' World Commission on Environment and Development [29]. The UN establishes that sustainable development refers to satisfying the needs of the present without compromising the resources of future generations. Academics from different disciplines, such as agriculture, economics, politics, and management, among others, have made efforts to concretize the concept of sustainability [30][31][32][33][34]. Specifically, in the field of management, there is a broad consensus in understanding that sustainability implies the development of business activity, creating value not only at an economic level but also at a social and environmental level [35]. Thus, sustainability is widely accepted as having three overlapping dimensions: the simultaneous pursuit of economic prosperity, environmental quality, and social equity [12].
Although sustainability in its origins was fundamentally focused on environmental factors, the concept of sustainable development has since been expanded to include the consideration of the social dimension as a fundamental element of development. This extension of the concept of sustainability to emphasize the economic and social dimensions is reflected in the objectives of the 2030 Agenda for Sustainable Development of the UN. Of the 17 principles established by the UN, a large number of them make direct reference to the improvement of society through the reduction of poverty, hunger, and gender inequality, and the improvement of health and well-being, education and decent work. Decent work was defined by the ILO in 1999 as being based on the principles of freedom, equality, security, and human dignity [35]. According to the ILO, decent work covers four main dimensions: employment, social protection, workers' rights, and social dialogue [36].
Decent working conditions facilitate dignified living conditions, which create value not only at the individual level but also at a social level since it reduces poverty and inequality and improves the quality of life and health of society as a whole [37]. Furthermore, decent job conditions improve business results through work engagement [20][21][22]. Work engagement is defined as an active and positive state that entails an attitude of vigor, action, and absorption towards the assigned roles in the workplace [20]. Vigor is reflected in high levels of energy and resilience to work, while dedication refers to being highly involved and enthusiastic about the job. Finally, absorption refers to the ability to fully concentrate on the task that is being developed at work [22]. Therefore, committed employees are those who are physically, cognitively, and emotionally connected to their work roles, as Kahn [38] indicates. It is necessary to distinguish committed workers from satisfied workers. While job satisfaction is a passive manifestation of well-being, work engagement goes beyond well-being to reflect an active state of pleasure and dedication to work [39]. This sense of commitment to the work not only generates benefits for the employees´health, but also encourages them to increase their effort and dedication to their work, contributing positively to generating benefits for the organization [21][22][23]39,40].
Presuming the positive relationship between decent work and work engagement and the benefits of employees´commitment to organizational performance, previous studies have investigated the factors that determine work engagement (e.g., [41][42][43][44]). These studies place special emphasis on individual management practices that enhance a supportive working environment [44]. In this vein, Anitha [41] focused on exploring how the working environment and employee relationships determine work engagement. Mokaya and Kipyegon [42] evaluated how several factors such as the performance management system, personal development and growth opportunities, and workplace recreation and remuneration influence employees´work engagement. De Cuyper et al [43] found that permanent contract was positively associated with an increase in work commitment and that permanent workers are more committed than temporary workers and vice versa. In the same line, Lo Presti and Nonnis [45] found that workers with permanent contracts showed higher levels of work engagement and that when their perception of job insecurity increased, their level of work engagement decreased and became similar to that of workers with temporary contracts. These results are explained because job insecurity is positively associated with psychological distress, which in turn negatively affects work commitment [46,47].
Despite the advantages generated by decent working conditions, these are being threatened by the processes of globalization of the economy and by the economic recession of recent years [48,49]. Both have promoted the employment precariousness through work arrangements in which flexibility predominates over stability and have led to an increase of dependent self-employed. [14]. The limited legal relationship of these workers with the company for which they provide services makes the nature of their work more precarious in comparison to other occupational categories, what presumably leads to lower levels of work engagement among dependent self-employed [23].
Investigations that deepen the study of dependent self-employed are scarce. Previous studies in this field focus on two fundamental research lines. On the one hand, previous studies were centered on the identification and measurement of this occupational category (e.g., [50][51][52][53][54][55][56]) On the other hand, other studies focused their efforts on analyzing whether there were differences at the personal and professional levels between this category and non-dependent self-employed and wage earners (e.g., [53,57,58]).
Regarding the first line of research focused on the identification and measurement of dependent self-employed, Williams and Lapeyre [18] pointed out that the dependent self-employed are being falsely classified as self-employed by employers (when they should be classified as wage earners) with the aim of circumventing collective agreements and labor regulations. This allows employers to pay fewer taxes, to avoid obligations in terms of minimum salary, the maximum number of working hours legally allowed per week for employees, etc. In this line, Taylor [59] highlights that falsely classifying wage earners as self-employed is common in technology companies that base their activity on online platforms, in the construction sector, and in the financial services industry. Furthermore, the literature indicates that the dependent self-employed present low levels of professional qualification and are the first to be dismissed in times of restructuring [53]. In addition, the likelihood of moving from employee to dependent self-employed increases if the worker works part-time for a year or more, while it decreases if he/she occupies supervisory positions, which suggests that the dependent self-employed are usually located in the lower part of the occupational hierarchy [53][54][55][56].
Regarding the research line focused on comparing dependent self-employed with other occupational categories, Böheim et al. [53] observe a wide gap between the different labor figures in term of working hours. They argue that the non-dependent self-employed work an average of 41 hours per week, wage earners 34 hours, and dependent self-employed work 37 hours per week. The literature shows that the labor situation of dependent self-employed may differ from the conditions of the rest of the occupational categories since legislation in terms of employment protection, taxation, and social security are also different across categories (e.g., [60][61][62][63][64][65][66][67][68]).
Despite the value provided by these studies, most of them either consider only some aspects related to working conditions that can influence work engagement, or rely on small samples focused on a single occupational category. The investigations that focus on comparatively analyzing the group of dependent self-employed with the rest of the categories are scarce. The present research explores the working conditions of the three occupational categories-dependent self-employed, non-dependent self-employed, and wage earners-and analyses the influence of those working conditions on their work engagement.

Development of a Structured Framework for the Study of Work Engagement
In order to develop a structured framework of analysis to study the relationship between decent work and work engagement, we have taken as a basis the Sixth EWCS (2015). This survey identifies seven dimensions related to decent work that can affect work engagement: physical environment, work intensity, working time quality, social environment, skills and discretion, prospects, and earnings.

Physical Environment
This dimension encompasses the physical risks suffered by workers at their jobs. Decent work necessarily implies safe work in physical terms [69]. Aspects such as ergonomic risks, ambient, biological, and chemical hazards are highly relevant in employee health [70]. A safe physical environment is associated with an improvement in personal growth, learning possibilities, and the professional development of workers [71]. That is why an adequate physical environment can increase the level of energy with which employees perform their job tasks and their resilience to the problems that may arise in the workplace, as well as their ability to fully concentrate on tasks-all of which are fundamental aspects of work engagement [22].

Work Intensity
The intensity of labour demands associated with the performance of a job is important to work engagement because these factors play a significant role in employees' ability to concentrate, which is reduced by long working hours [20]. A job that demands work at a very high speed, working to tight deadlines, and which requires high emotional demands (such as being in situations that are emotionally disturbing), among other aspects, creates a work environment that prevents motivation, and subsequently negatively influences work engagement [41].

Working Time Quality
A decent work schedule is a determining factor in the levels of work engagement. The organization and length of working time interfere with the possibilities of balancing the work life and personal life of employees [72]. Work characterized by long working hours, shift work, unsocial hours, night work, etc., creates difficulties in work-life balance, which generates work stress and decreases the levels of commitment of employees within the company, since they consider that their personal needs are not being heard by the employer [73]. On the contrary, a flexible working time in which employees can decide on different work schedules that are more suitable for them enhances employees' commitment towards the company and the job itself [74].

Social Environment
This dimension measures the degree to which workers perceive social support from their peers and superiors. The quality of the social environment at work is a fundamental aspect that determines the level of work engagement of employees since the social support of the bosses and colleagues influence the workers' perception with respect to the justice at the workplace [3,75]. The perception of justice increases the levels of work engagement with their employer [76,77]. On the contrary, a social environment characterized by physical, sexual, and/or verbal abuse has a negative influence, not only on employees at the individual level in terms of health, but also on their level of work engagement [78].

Skills and Discretion
Skills and discretion refer to the skills necessary for the performance of certain work activities and to the autonomy employees have to use those skills in the workplace. On the one hand, providing the workers with the necessary training to adequately perform their functions becomes a key element that affects their motivation and commitment [79]. On the other hand, autonomy encourages the employees' proper relationship with their job, favouring their work commitment [80].

Prospects
Job security and the prospects of career advancement are configured as a dimension of decent work that directly contributes to satisfying workers´material and psychological needs related to their self-esteem [81]. Healthy self-esteem makes workers show high levels of enthusiasm and resilience in their job, which favours work engagement [79]. As indicated by Ballout (2009), those employees that are more committed to the company are those to whom the company provides with more stable employment and with possibilities of career advancement [82]. On the contrary, the lack of job security and/or career opportunities generate lack of commitment, and consequently, high levels of turnover [83].

Earnings
Wage becomes one of the most important material factors that determine work engagement [84]. Van Aerden et al. [84] argue that an adequate salary is a factor that positively influences work engagement since it allows employees to cover their needs, not only personally, but also family related, and to maintain their social status. Workers' perception that their economic rewards are in accordance with their efforts at work reinforces the psychological contract with the employer, enhancing work commitment [85].
According to the aforementioned, each of these seven dimensions contains a large number of individual indicators that allow a systematic and holistic analysis of decent work in relation to work engagement. This framework of analysis is proposed with the objective of comparatively analysing how decent work influences the levels of work engagement of dependent self-employed compared to the most common occupational categories in Europe: non-dependent self-employed and wage earners.

Research Purposes
The present research aims, on the one hand, to explore a decent job in Europe by analyzing whether working conditions are more precarious in the group of dependent self-employed in comparison with the rest of the main occupational categories. On the other hand, this research analyzes whether there is a positive relationship between decent work and work engagement and whether this relationship varies among the different occupational categories under analysis. To this end, an empirical study has been designed with two main research purposes.
(1) First, a comparative descriptive analysis will be undertaken to establish whether the job is less decent in the group of dependent self-employed with respect to non-dependent self-employed and wage earners. (2) Second, a statistical analysis will be performed to analyze how decent work conditions influence the level of work engagement of these occupational categories.

Sample
This research used self-reported features of working conditions from the sixth European Working Conditions Survey (EWCS) to build seven separate indices of decent job [13]. The sample is a multistage, stratified, random sample of the working population in each country. The interviews were conducted face to face in people's homes, with an average duration of 45 minutes, and in the national language(s) of the country. The EWCS has been widely employed to explore working conditions in the European context because of its multidimensional nature (e.g., [86][87][88][89]). This survey delves into the working conditions of European workers, offering a comprehensive overview of decent work that comprises seven dimensions: physical environment, work intensity, working time quality, social environment, skills and discretion, prospects, and earnings by occupation, sector, and age group [24].
To evaluate the relationship between work engagement and decent work, the analysis was performed for dependent self-employed, non-dependent self-employed, and wage earners. In the EWCS, a total of 42,963 workers were surveyed, of which 0.03% were dependent self-employed (N = 1693), 13.73% were non-dependent self-employed (N = 5902), and 82.32% were wage earners (N = 35,368). Table 1 shows the descriptive statistics and bivariate correlations of the research variables. The average level of work engagement of the sample was 71.2 out of 100. The highest values of the dimensions of decent work were observed in the physical environment (82.9), working time quality (80.9), and social environment (78.1). Table 1 also shows that most dimensions of decent work correlated with each other and with the dependent variable (work engagement). Work engagement presents a positive and significant correlation with all the indices considered.

Measures
Work engagement is the dependent variable in this research. It is constructed from six variables included in the EWCS: The use of this survey to analyze work engagement is based on previous research that indicates its validity and reliability to measure work engagement [90].
The independent variables are the seven dimensions of the quality of work of the EWCS. These indices are formed by a wide range of variables that constitute decent work. The results can be interpreted as a synthetic measure of decent employment as a whole formed by the seven dimensions of the index, which also provide information about the individual variables that shape each dimension of decent work [38]. Each of the scales is formed by questions designed to obtain a score of the objective properties of the job performed by the respondents (see Table 2).

Data Analysis
First, a descriptive analysis of a decent job (considering the seven dimensions of the quality of work) was developed for the different occupational categories under analysis. Second, three linear regression models (for dependent self-employed, non-dependent self-employed, and wage earners) were estimated using the forward step method of entering variables in the equation. The default criteria of p < 0.05 was used to this aim. The complete work engagement model can be observed below: Work engagement = β 0 + β 1 Pe + β 2 Wi + β 3 Wtq + β 4 Se + β 5 Sd + β 6 Pr + β 7 Ear + ε NOTE: Pe (Physical environment), Wi (Work intensity), Wtq (Working time quality), Se (Social environment), Sd (Skills and discretion), Pr (Prospects) and Ear (Earnings).

An Overview of the Job Quality Index
The values obtained for the seven dimensions of decent work are presented in Table 3. The results indicate that dependent self-employed have more precarious working conditions than the rest of the occupational categories in most of the indexes analyzed, with two exceptions: the index of work intensity-the most precarious situation is observed in the group of wage earners-and work time quality-the most unfavorable situation is presented by non-dependent self-employed. It is remarkable the significant wage gap observed among the different groups, which is especially wide between dependent and non-dependent self-employed, with a difference of 651 euros per month. Similarly, it occurs with respect to the level of work engagement of dependent self-employed compared to the rest of the groups, which show a lower average value (66.5 points) than non-dependent self-employed and wage earners. The highest levels of commitment were observed in non-dependent self-employed (73.9 points), followed by wage earners (71 points). (1) Physical environment, (2) Work intensity, (3) Working time quality, (4) Social environment, (5) Skills and discretion, (6) Prospects, (7) Earnings.

Decent Job and Work Engagement
The relationship between decent work and work engagement is expected because decent work is a measure of how working conditions meet multiple human needs. Consequently, the satisfaction of these needs will result in a greater or lesser degree of commitment. Considering that the dependent self-employed show less decent working conditions than non-dependent self-employed and wage earners, it is of interest to analyze the relationship between decent work and work engagement comparatively in the three occupational categories. This will allow for drawing conclusions on how the dimensions of decent work impact work engagement in each occupational category.
To explore whether there is a relationship between work engagement and the seven dimensions of decent work, a linear regression model was performed for the occupational categories (see Table 4).
Analyzing in detail each of the indices that influence work engagement, it was observed that the physical environment significantly influences the work engagement in the three occupational categories. Specifically, this variable exerts a greater influence on the work engagement of dependent self-employed (β = 0.206) in comparison to non-dependent self-employed (β = 0.116), and wage earners (β = 0.085). However, in the case of wage earners and non-dependent self-employed, the work intensity is a relevant dimension in work engagement, unlike what happens in the group of dependent self-employed. With regard to the working time quality, these indices does not determine the work engagement of dependent self-employed, while it is determinant of work engagement in the case of wage earners (β = 0.030) and non-dependent self-employed (β = 0.021). The social environment index exerts a stronger influence on work engagement in the case of wage earners (β = 0.129) in comparison to the rest of groups (β = 0.058 and β = 0.068 in the case of dependent self-employed and non-dependent self-employed, respectively). The construct that measures the skills necessary for the performance of the job and the autonomy exerts a significant influence on the work engagement, being this slightly more relevant in the group of dependent self-employed (β = 0.174) compared with the rest of the workers (β = 0.106 and β = 0.067 in non-dependent self-employed workers and wage earners, respectively). The prospects index exerts a significant and relatively high influence-in comparison with the other dimensions of decent work-on the work engagement of all employee groups. However, this influence is slightly higher in the case of non-dependent self-employed (β = 0.147) compared to dependent self-employed workers (β = 0.141) and wage earners (β = 0.127). Finally, in relation to earnings, it was observed that although this dimension exerts a significant influence on the work engagement for the three occupational categories, this influence is relatively low compared to the rest of the variables, with all β close to 0. Table 4. Work engagement regression models (dependent self-employed, non-dependent self-employed, and wage earners).

Dependent Self-Employed Model
Non-Dependent Using all the predictor variables together to evaluate which combination is the most efficient to explain work engagement, it can be observed that all the dimensions of decent work have a significant influence on work engagement in the case of non-dependent self-employed and wage earners. However, in the case of dependent self-employed, work engagement was determined only by the dimensions of physical environment, social environment, skills and discretion, prospects, and earnings. Therefore, these dimensions are configured as influential in the work engagement in all the occupational categories. Work intensity and working time quality were presented as determinant variables in the case of non-dependent self-employed and wage earners, but not in the case of dependent self-employed. Specifically, in the case of dependent self-employed, the dimension that most influences work engagement was physical environment (β = 0.206), while in the case of non-dependent self-employed the most influential dimension was prospects (β = 0.147) and in the case of wage earners was the social environment (β = 0.129). Finally, regarding the control variables, age was presented as a factor influencing the level of work engagement of non-dependent self-employed and wage earners. Likewise, the educational level was presented as a variable that significantly influences work engagement, but only in the case of non-dependent self-employed.

Discussion and Conclusion
The analysis of sustainable development involves a great complexity because it covers different areas that must be developed in a balanced way such as the economy, society, and the environment, especially taking into account that resources are limited. Although originally the majority of the studies on sustainable development focused on aspects fundamentally related to economic development and the protection of the natural environment, this vision has been extended to other areas to emphasize the relevance of human development and the enhancement of societies´quality of work and life, as extracted from the UN's objectives of sustainable development [91,92]. Recent literature considers sustainability not only from an ecological and social point of view, but also in terms of decent work, as indicated by Di Fabio [21]. Decent working conditions that allow workers to balance work and personal life, develop personally and professionally, etc., become an important concern for academics, professionals, and policy-makers. This is because decent work not only contributes to enhancing work and life quality but also because it becomes an important factor in organizational performance through the mediating role of work engagement. Having committed employees becomes especially important for contemporary organizations since it becomes a highly determinant factor in the long-term organizational success. Decent working conditions highly influence the level of employees' commitment to their job since it leads to a positive, high-energy affective-motivational state combined with high levels of dedication and a strong focus on work [20]. Work engagement is a good predictor of employee health, work performance, creativity, organizational citizenship behavior, and customer satisfaction, which subsequently affects positively to organizational performance [39,40]. On the contrary, if workers consider that their job is precarious or indecent, they face numerous stressors that negatively influence their psychological well-being, and consequently, their levels of work engagement [93].
The processes of globalization and economic crisis of recent years have led to the fragmentation of the labor market and the emergence of occupational categories in which precariousness predominates. The occupational categories characterized by precarious working conditions, particularly dependent self-employed, have proliferated in recent years in Europe since, in some countries, the austerity measures have led to changes in the labor market that have prioritized flexibility over sustainability. As a result of structural reforms that have been implemented in Europe to overcome the economic recession, a double threat has emerged. On the one hand, the labor market has favored the increase of occupational categories where precariousness has been normalized through "non-standard" forms of employment (which present high job insecurity). On the other hand, contractual terms and working conditions in terms of working hours, wages, etc., have become less favorable for workers [94]. As a consequence, a scenario where precariousness predominates as a norm is observed in the European context [95]. Assuming that working conditions are determinant in work engagement, it is expected that the different occupational categories present differences in their levels of work engagement, widening this gap as work becomes more precarious. Particularly, dependent self-employed sometimes hide questionable labor practices [96].
The question that underlies this research is the following: Is the European Union truly sustainable in the long term when it allows the development of occupational categories in which precariousness prevail? This study aims to emphasize the need for Europe to return to the path of sustainability through decent working conditions, what might enhance not only the quality of life of its citizens, but also the organizational performance of its companies.
In order to contribute to this end, wide-ranging empirical research has been developed, which adopting a holistic and systematic approach has allowed the development of a comprehensive vision of the factors that underlie decent work in the different occupational categories predominant in Europe (dependent self-employed, non-dependent self-employed, and wage earners).Furthermore, this research has allowed the identification of the dimensions of decent work that have a greater impact on work engagement. This investigation might contribute to the analysis of the labor market and the public policies in Europe, especially taking into account the objectives of human development recently identified the UN [97].
The results have confirmed the research purposes. First, it has been shown that there are three differentiated occupational categories in Europe (dependent self-employed, non-dependent self-employed, and wage earners) with differing levels of employment quality. The dependent self-employed category presents more precarious working conditions than the rest. Considering that their working conditions are less decent than the rest of the categories, this group presents the lowest levels of work engagement. The low levels of work engagement of dependent self-employed are explained because their working conditions are worse in general, with the exception of the labor intensity and the working time quality dimensions. This can be explained by the fact that part-time work in the group of dependent self-employed workers was higher (35.92%) compared to the rest of the categories (17.61% and 18.82% in non-dependent self-employed and wage earners, respectively). The more favorable levels of work intensity and work time quality among dependent self-employed are in comparison to the rest of categories can be explained by the high levels of precariousness of dependent self-employed. This can be concluded when an in-depth analysis of several additional variables in the EWCS is performed. For instance, regarding the question whether they became self-employed due to their own choice or because they did not have better alternatives, 41.87% of dependent self-employed indicated that they had no other alternative compared to 22.91% of the non-dependent self-employed. This is in consonance with the question that indicates if their schedule adjusts to their personal life; 82.22% of the dependent self-employed indicate yes, while this percentage was lower (77.45%) in non-dependent self-employed. Furthermore, the most favorable working conditions of wage earners in all of the majority of the dimensions of decent work have contributed to widening the gap between the different occupational categories. For instance, the monthly net earnings of dependent self-employed are lower (793 euros) than those of the non-dependent self-employed (1444 euros), and wage earners (1338 euros). These results reflect a fragmented labor market, and in the case of the dependent self-employed, high levels of precariousness. In particular, this study reveals that the labor reality of this group is not very sustainable since it does not meet at least two of the Sustainable Development Goals: Goal 3, focused on ensuring healthy lives and promoting the well-being of all ages, and Goal 8, commitment to decent work.
Second, given that one of the essential objectives of European policy is the promotion of workersh ealth and wellbeing because they affect, not only the physical and mental health of individuals but also to job performance [90], it was of great interest to investigate the relationship between decent work and work engagement in the European context. From this perspective, regression models have confirmed the significant influence that decent work has on work engagement. Specifically, factors related to the physical environment, social environment, skills and discretion, prospects, and earnings are determinants in the levels of work engagement of employees of all occupational categories (dependent self-employed, non-dependent self-employed, and wage earners). The results show that previous dimensions of decent work are common for the enhancement of work engagement among the three categories. The results also indicate that the physical environment is worse in the case of dependent self-employed than in the rest. A similar situation is observed in regards to the social environment, which is also worse for dependent self-employed. This indicates that the work of dependent self-employed takes place in a less friendly social environment than in the case of non-dependent self-employed. Regarding the skills and discretion index, the results show that it exerts a positive influence on the work engagement of the dependent self-employed, suggesting that granting more control and attributions to workers contributes positively to work engagement [98][99][100][101]. Finally, the work intensity and working time quality also exert a positive influence on work engagement and are the variables in which the dependent self-employed are in a better situation with respect to the rest of the groups. This circumstance might be explained by the fact that part-time work is more frequent in this group so that their working hours tend to be less intense, while they have more possibilities to manage their working hours.
Taking into account that the working conditions of dependent self-employed are comparatively worse than the rest, it is expected that they show a lower degree of work engagement. Within this category, it is remarkable that the work-engagement is influenced by up to five of the seven dimensions of decent work (physical environment, social environment, skills and discretion, prospects, and earnings). The other two dimensions of decent work (work intensity and working time quality) are influential in work engagement for the rest of the occupational categories.
This study has important practical implications, since it highlights the differences in working conditions among the main occupational categories and emphasizes the precariousness of dependent self-employed with respect to the rest of the categories. In addition, it identifies which dimensions should be improved by public policies and private practices in order to move towards more decent working conditions. Specifically, this study has overcome a traditional barrier to policy development: the difficulty of measuring and comparing decent work [102]. This research has developed a systematic and holistic analysis of the differences of working conditions across occupational categories, as well as the direct effect of a decent job on work engagement. The results obtained contribute to the visualization of the existing fragmentation of the labor market, which hinders sustainable development. Hence, the study can be useful for policymakers to become aware of the need to adopt legislative measures.
This research points to the need to ensure long-term sustainability in Europe through the development of a preventive approach aimed at guaranteeing decent work, since it is key to sustainability, growth, and success of both workers and organizations [11]. Hence, it is imperative that a minimum framework is developed to ensure decent work. In turn, this research can be useful for organizations to realize the need to move to a more sustainable framework of working conditions. Although the adoption of sustainable management models is a duty in itself (since it contributes to creating individual and societal value), it is evidenced that it can also be an instrument to improve organizational performance through the role that decent job plays on work engagement [103].

Limitations and Future Directions
Despite the advantages presented by the data used in this research, some limitations must be highlighted, mainly regarding methodological issues. First, the measures of the EWCS are self-reported, so they may present a certain bias-motivated by the social desirability implicit in some questions. This bias may be especially important in the case of salaries, work histories, the type of contract, social relationships with colleagues and/or supervisors, as well as other sensitive issues in the work environment that may be affected by conscious or unconscious biases that arise from perception of the workers of what "they would like it to be" in comparison with the standard of living of the country, economic conditions, etc. Second, in spite of including a wide battery of variables, the study developed was cross-sectional in nature and subject to the shortcomings that this entails. Finally, the research was developed in a specific geographical area, so we must be careful when generalizing the results obtained. Future research could focus on comparatively exploring the three occupational groups in different geographical areas that present significant institutional differences with respect to the European context.

Conflicts of Interest:
The authors declare no conflict of interest.