*2.2. Participants*

In all, 783 young Spanish respondents were selected for this study. This sample is representative of all the regions in Spain. As mentioned above, the ages of the participants ranged from 16 to 30 years old (*M*age = 25.21, *SD* = 3.40), with slightly more females (52%). Most of the participants worked in the private sector (82%), and most of them had a temporary contract (58%).

## *2.3. Variables/Instruments*

Job satisfaction was assessed as the composite of extrinsic, intrinsic, and social job satisfaction [35]. This measure can be applied to a wide range of jobs. Extrinsic job satisfaction was measured with seven items. A sample item is: "Indicate your level of satisfaction with your schedule". Intrinsic job satisfaction was measured with seven items. A sample item is: "Indicate your level of satisfaction with the variety of tasks to perform". Finally, social job satisfaction was measured with five items. A sample item is: "Indicate your level of satisfaction with your coworkers". All items were scored on a 5-point Likert scale (from 1 = *not at all* to 5 = *very much*). The three subscales had good reliability, α = 0.86 (extrinsic job satisfaction), α = 0.91 (intrinsic job satisfaction), α = 0.80 (social job satisfaction), and α = 0.94 (for the composite of the three subscales).

Items measuring health belong to the scale of the General Health Questionnaire, developed by Banks [36] in young community sample. The reliability of the 12 items reported by Banks [36] was α = 0.76. In the current study, we applied four items with higher factor loadings to measure employees' health. A sample item is: "In the last few weeks I have noticed being constantly overwhelmed and under stress". The respondents answered on a 5-point Likert scale (from 1 = *strongly disagree* to 5 = *strongly agree*). The scale showed good reliability (α = 0.76).

Job importance was assessed as the composite of extrinsic, intrinsic, and social job importance [37]. We chose 19 items to measure job importance provided by England and Harpaz [37]. Items were preceded by the phrase "Please, indicate the importance that each of the following aspects of the work has for you"; sample items for each facet are: "Security at work"; "Useful work for society"; "Meaningful work that makes sense to do." The respondents answered on a 5-point Likert scale (from 1 = *nothing* to 5 = *a lot*). The scale showed good reliability (α = 0.89).

Role ambiguity was measured with the scale provided by Rizzo et al. [19]. The original reliabilities, reported by Rizzo and colleagues in two different samples were good (α = 0.82). In the current study, we selected three items with higher factor loadings to measure role ambiguity. A sample item is: "I know how and what my responsibilities and competencies are at work". The respondents answered on a 5-point Likert scale (from 1 = *strongly disagree* to 5 = *strongly agree*). We performed reverse-scoring of the three items. This scale showed good reliability (α = 0.80).

Role conflict was measured with the scale provided by Rizzo et al. [19]. The original reliabilities in two different samples were α = 0.82. In this study, we selected three items with higher factor loadings to measure role conflict. A sample item is: "I receive incompatible requests from two or more people". The respondents answered on a 5-point Likert scale (from 1 = *strongly disagree*, to 5 = *strongly agree*). This scale also showed a good reliability (α = 0.75).

Role overload was measured with the scale of perceived work overload, proposed by Cooke and Rousseau [38]. In the current study, we selected three items with higher factor loadings. A sample item is: "I have too much work to do everything well". The respondents answered on a 5-point Likert scale (from 1 = *strongly disagree* to 5 = *strongly agree*). This scale showed a good reliability score in this study (α = 0.82).

Overqualification was measured with the item: "If an individual had to perform your job, what level of education would you recommend him or her to have?" Participants responded on a 12-point scale of the International Standard Classification of Education—ISCED ((from 1 = no studies (ISCED level 1) to Doctorate (ISCED level 12)). We also considered the individual level of education and transformed both the recommended level of education and the individual level of education into years of education. To determine whether an employee was overqualified, the recommended level of education was subtracted from the level of education achieved. Negative and zero scores were considered indicators of education under-qualification and match, respectively, and positive scores were considered indicators of overqualification [25]. In our study, 21.7% of the participants were overqualified, which is similar to the rate (21.5%) of overqualification across Europe [25].

To eliminate some alternative explanations, we considered some variables that could affect our outcome variables and therefore we controlled for gender (0 = male, 1 = female), type of sector (0 = private, 1 = public), type of employment/contract (0 = temporal, 1 = permanent), and age (in years). We describe in detail the choices and procedures related to the control variables in order to ensure transparency and facilitate the reproducibility of the results [39].

In terms of gender, previous studies show that relatively to men, women tend to report higher levels of depression, but that the positive relationship between the efforts to fulfill work role demands (which interfere with employee's ability to fulfill family demands) and depression is stronger among men [40]. In terms of type of sector and age, previous studies also show that public organizations are good in fulfilling their promises to young employees i.e., their psychological contract, and that this is translated into improved job satisfaction [41]. Considering the type of contract, previous studies also suggest that permanents as compared with temporaries engage more in relational psychological contracting, therefore, when this is violated (e.g., by producing job insecurity), this compromises more the job satisfaction for permanents than for temporaries [42]. Finally, previous research [43] also shows that temporary employees report higher wellbeing (e.g., mental health).
