An Analysis of the Differences Between Unionised and Non-Unionised Workers in Psychological Well-Being, Job Satisfaction, and Life Satisfaction: A Study in Organisations Located in the Basque Country

Abstract

Given the limited literature on the association between trade unions and mental health, this study aims to analyse differences between unionised and non-unionised workers in terms of psychological well-being, job satisfaction, and overall life satisfaction. These differences were analysed based on a sample of 260 workers from organisations located in the Basque Country, of whom 144 were members of a trade union and 116 were not. Our results suggest significant differences between unionised and non-unionised workers in terms of autonomy (t = 3.10; p < 0.01), environmental mastery (t = 2.20; p < 0.05), and personal growth (t = 2.10; p < 0.05), with trade union members demonstrating higher mean scores in all three metrics than their non-unionised counterparts. The results also revealed significant differences in job satisfaction (t = −0.31; p < 0.01), although non-unionised workers scored higher than their unionised counterparts. Contrary to expectations, no differences were found between the groups in relation to overall life satisfaction. After discussing the results, the main limitations of the study are described, and some proposals are made for future research.

1. Introduction

The traditional pathway open to workers who wish to join forces to defend their well-being in the workplace is by forming and/or participating in trade unions (Hagedorn et al. 2016). Trade unions contribute to workers’ health through a variety of different structural and interpersonal channels. Collective bargaining and union activity often focus on workplace benefits, safer conditions, and the distribution of productivity within the organisation. Consequently, there is a strong consensus concerning the pathways that link trade unions to public health through wages, income equality, the reduction in hazardous working environments, and the promotion of social cohesion and solidarity at work (Leigh and Chakalov 2021).

Basque trade unionism has its roots in the labour movement of the late 19th century, with an evolution marked by industrialisation, the Spanish Civil War, and the subsequent dictatorship, which forged a diverse movement with a strong nationalist bent. The first attempts to organise workers in the Basque Country in the late 19th century were driven by anarchists and socialists (UGT) in response to the harsh working conditions of the growing industrial sector. The influence of socialism in the region, particularly in mining and industrial areas, was significant from the outset. A key milestone in this timeline was the founding of Solidaridad de Obreros Vascos (ELA-SOV, in Basque and Spanish) in Bilbao on 23 July 1911. Promoted by the Basque Nationalist Party (PNV), it aimed to create a specifically Basque trade union, thereby counteracting the influence of the UGT and other state-level organisations. In 1933, it changed its Spanish name to Solidaridad de Trabajadores Vascos (STV).

The Spanish Civil War and Franco’s subsequent dictatorship (1939–1975) were a period of repression and clandestinity for trade unions, which were outlawed with the exception of those controlled by the regime (the Vertical Union). ELA suspended its public activities and remained underground for almost 40 years. Other unions, such as UGT and CCOO, also operated clandestinely, playing an important role in opposing the regime. After Franco’s death and Spain’s transition to democracy, Basque unions regained their legal status. In 1977, ELA regained its legal status, and in 1980, it became the most represented union in union elections, a position it has maintained ever since. Comisiones Obreras de Euskadi (CCOO de Euskadi) and Unión General de Trabajadores del País Vasco (UGT Euskadi) are also important players in the trade union landscape, although the nationalist unions ELA and LAB tend to have a more prominent representation compared to unions at the national level (Kaiero Uría 1991; Miralles 1992).

Today, Basque trade unionism is characterised by its diversity, with Basque-based unions (ELA, LAB) and other national unions with a presence in the Basque Country (CCOO and UGT), which actively participate in collective bargaining and in demanding a Basque framework for labour relations (García Lerma and Aparicio Rodríguez 2022).

2. Literature Review and Hypothesis Development

Although there is a growing body of empirical literature on the association between trade union membership and physical health (Leigh and Chakalov 2021; Malinowski et al. 2015), research into the link between trade unions and mental health is still scarce. Given that all the aims of traditional trade union organisations and activism focus on making a positive contribution to the well-being of individuals and families, a surprisingly low number of psychology research studies have focused on documenting its benefits on the individual psyche (Carriere 2020; Lott 2014; Sami 2022; Ulacia 2024; Ulacia et al. 2022). According to the research that has been conducted, the influence of trade unions is not limited to ensuring only financial well-being, but they also have a direct impact on many other variables, including psychological well-being (Carriere 2020; Chawla et al. 2018; Lott 2014; Ulacia et al. 2025), respect and dignity (Carriere 2020; Zweig 2004), self-esteem and autonomy (Carriere 2020; Fuller and Hester 2001; Pacek 2009; Rosenberg 2009), empowerment and personal development (Hogler et al. 2015; Lee et al. 2017; Malinowski et al. 2015), and trust, camaraderie, and social connection (Carriere 2020; Chawla et al. 2018; Mann 2011; Mellor 2017; Pacek 2009). Moreover, several studies have suggested that trade union membership significantly improves job satisfaction (Artz 2010; Chawla et al. 2018; Peetz 2012; Ulacia et al. 2025), satisfaction outside the workplace (Carriere 2020; Cobble 2007; Rosenberg 2009; Terríquez 2011), and overall life satisfaction (Coshow and Radcliff 2009; Flavin and Shufeldt 2016; Lott 2014; Ulacia et al. 2025).

According to Díaz et al. (2006), the study of psychological well-being has mainly focused on indicators of positive functioning. Its early iterations were rooted in concepts such as self-actualisation, maturity, and full functioning, as developed by Maslow (1968), Allport (1955), and Rogers (1951), despite repeated questions about the validity and reliability of the methods used by these authors. Their ideas, however, paved the way for other psychologists interested in identifying points of convergence and moving towards an explanatory model of psychological well-being. It is worth highlighting that the model proposed by Ryff (1989) some years later is known as the ‘Model of Constructional Multidimensionality’ or the ‘Multidimensional Model of Psychological Well-being’. The model was established after the author, together with Keyes (1985), identified six clearly differentiated dimensions that make up the concept of well-being: self-acceptance, positive relations with others, autonomy, mastery of one’s environment, purpose in life, and personal growth. To the best of our knowledge, this model of well-being has never before been applied to the study of trade union membership in the sense that, although each of the dimensions has been studied independently, they have never been analysed as a whole.

First, self-acceptance is one of the key criteria for well-being. Despite being aware of their own limitations, people tend to try to feel good about themselves. Having a positive attitude towards oneself is a fundamental characteristic of positive psychological functioning (Keyes et al. 2002). Several authors have argued that belonging to a trade union provides an individual with the opportunity to gain control and power over some aspects of their work and family life, thereby enhancing self-esteem and, consequently, self-acceptance (Carriere 2020; Fuller and Hester 2001; Hagedorn et al. 2016; Lott 2014; Rosenberg 2009). Second, people need to maintain stable and positive relationships and have friends they can rely on. The capacity to love is a fundamental component of well-being and mental health (Ryff and Singer 1998). Hagedorn et al. (2016) argue that trade unions foster well-being by encouraging democratic engagement and creating a sense of community among workers. They also help strengthen social support networks, interpersonal connections, a sense of solidarity, and, ultimately, a more active social life (Becker et al. 2024; Lott 2014). Third, in relation to autonomy, people need to be grounded in their own convictions and maintain their independence and personal authority. Autonomous individuals are able to better resist social pressures and self-regulate their behaviour (Ryff and Keyes 1995). Trade unions offer workers the opportunity to exercise greater control over various aspects of their personal and family lives, thereby promoting higher levels of independence and autonomy (Carriere 2020; Lott 2014; Rosenberg 2009). Fourth, environmental mastery refers to the ability to choose or create environments that are conducive to satisfying one’s desires and needs. People with high levels of environmental mastery have a greater sense of control over the world and feel that they are able to influence their surroundings (Keyes et al. 2002). Being a member of a trade union helps ensure that marginalised voices—including those of women (Kirton 2017), immigrants (Bada et al. 2018), and other minorities (Sweetman 2018)—are heard while at the same time increasing their capacity to right wrongs (Mann 2011). Having a clear group ‘voice’ and engaging in collective action generates a sense of empowerment, which in turn contributes to an increased sense of control over one’s environment, including a greater sense of job security (Becker et al. 2024). Fifth, people need to have a purpose in life and to set themselves goals that give their lives meaning. In this regard, belonging to a trade union enables individuals to set positive goals for themselves and achieve them through planned action (Lott 2014; Mann 2011; Pacek 2009). Finally, psychological well-being also requires the desire to develop one’s potential and grow as a person (Keyes et al. 2002). Several studies highlight the role that trade unions play in improving the communication, social, and problem-solving skills of their members, as well as in helping develop more informed and active citizens (Becker et al. 2024; Radcliff 2005).

For its part, job satisfaction is a construct that has attracted much attention from organisational behaviour specialists and is considered a strategic asset due to its favourable impact on organisational outcomes and employee well-being. At an organisational level, the evidence reported to date suggests that having satisfied workers is tantamount to having committed and motivated employees. At a personal level, thanks to a kind of ‘contagion’ effect, job satisfaction has been observed to spread to other areas of life, generating satisfaction with family and life in general (Carlson et al. 2014). Conceptually, job satisfaction has been defined from both an affective and cognitive perspective. According to the former, job satisfaction is considered a positive feeling experienced by an individual as a result of performing a job that interests them, in an environment that allows them to feel comfortable, and within an organisation that they find attractive (Judge and Klinger 2008). According to the latter, job satisfaction is viewed as an objective assessment or measurable judgement of one’s own work (Weiss 2002). In an attempt to overcome this dichotomy, Judge and Kammeyer-Mueller (2012) proposed a comprehensive definition that subsumes both aspects into an encompassing concept that has a broad consensus. However, instruments for measuring job satisfaction have, to date, focused solely on the cognitive dimension (Dalal and Credé 2013).

Much of the empirical evidence reported over recent decades supports the idea that trade union membership contributes significantly to individuals’ job satisfaction (Peetz 2012; Flavin and Shufeldt 2016; Chawla et al. 2018; Blanchflower et al. 2021). Despite this, there is much debate on the subject since the factors involved in the association between trade union membership and job satisfaction are multiple and complex. The meta-analysis conducted by Laroche (2016) suggests that this tension may stem from what the author defines as reverse causality; i.e., dissatisfied workers would be more likely to join trade unions in order to try to improve their unsatisfactory working conditions. It is also important to consider the effects of self-selection and socialisation processes (Bardi et al. 2014). Do people’s values align with those of organisations from the outset, implying self-selection based on values? Or do they change to better align with the appropriate and desirable values of those organisations, implying socialisation of values? In this regard, it is worth asking to what extent the level of job satisfaction among unionised workers is genuine or influenced by the need to conform to the values of their unions.

Other studies suggest that the relationship perceived by workers between trade union membership and job satisfaction may vary throughout the course of their lives. Studies such as those by Artz (2010) and Blanchflower et al. (2021) conclude that it is important to take into account the effect of the occupational and existential changes that workers may undergo at different stages of their lives. According to other authors, the substantial differences that exist between countries should be taken into account when studying the relationship between trade union membership and job satisfaction (Gumbrell-McCormick 2022; Hipp and Kolins Givan 2015). For instance, in a transnational study, Hipp and Kolins Givan (2015) found that the association between trade union membership and job satisfaction varies from country to country, depending on the political and social environment. Finally, according to the same study, being a member of a trade union also functions as a response mechanism that gives workers a channel through which they can voice their needs and preferences. The channelling of workers’ aspirations and proposals through trade unions has a positive effect on all factors influencing behaviour in the workplace, which, in addition to benefiting the company, also results in greater job satisfaction (Chawla et al. 2018; Peetz 2012).

Finally, life satisfaction is defined as an overall assessment made by an individual of their life (Pavot et al. 1991). According to this definition, when making this assessment, the individual examines all the tangible aspects of their life, weighing up the good and the bad, comparing this result with their own standards or criteria (Shin and Johnson 1978), and then reaching a conclusion about their general level of satisfaction with their life (Pavot et al. 1991). Judgements about satisfaction therefore depend on the comparisons that subjects make between the circumstances of their lives and what they consider to be a suitable standard. This last nuance is important because we are not talking about an externally imposed standard here but rather a self-imposed criterion. According to Diener (1984), research into life satisfaction should focus on the subjective judgements made by individuals about their own lives. In other words, rather than adding up satisfaction scores in specific areas to obtain a measure of overall satisfaction, it is better to ask the individual in question for an overall assessment of their life (Diener et al. 1985).

In general, few studies have attempted to analyse the effect of trade union membership on workers’ life satisfaction. Furthermore, although most conclude that belonging to a trade union has a positive effect on workers’ life satisfaction (Charman and Owen 2014; Flavin et al. 2010; Flavin and Shufeldt 2016; Lee 2022), some discrepancies can be observed, as some authors have failed to find any significant association between trade union membership and life satisfaction while others have found a negative correlation between the two (Becker et al. 2024; Charman and Owen 2014; Lee 2022). Some studies suggest that the association between trade union membership and life satisfaction is indirect in nature, with various explanatory mechanisms affecting the relationship (Becker et al. 2024; Bergagna et al. 2022; Flavin et al. 2010; Flavin and Shufeldt 2016; Lee 2022). One of the most studied of these mechanisms, for which strong mediating effects have been found, is job satisfaction. Several studies have concluded that trade union membership correlates positively with job satisfaction and that this in turn is positively associated with life satisfaction (Bergagna et al. 2022; Charman and Owen 2014; Flavin and Shufeldt 2016).

In order to contribute new evidence to this avenue of research, the present study analyses the differences between unionised and non-unionised workers in organisations located in the Basque Country in terms of self-acceptance, positive relations, autonomy, environmental mastery, personal growth and autonomy of psychological well-being (Díaz et al. 2006), job satisfaction (Schlett and Ziegler 2014), and overall life satisfaction (Pavot et al. 1991). We therefore posed the following hypotheses:

Hypotheses H1.

We expected unionised workers to have higher levels of psychological well-being in terms of self-acceptance, positive relations, autonomy, environmental mastery, and personal growth than their non-unionised counterparts.

Hypotheses H2.

We expected unionised workers to have higher levels of job satisfaction than their non-unionised counterparts.

Hypotheses H3.

We expected unionised workers to have higher levels of life satisfaction than their non-unionised counterparts.

3. Materials and Methods

3.1. Procedure

Prior to collecting the data, coordinators at each organisation were contacted and informed of the aims of the study. To clear up any possible doubts or queries, after they had given their approval, these same coordinators were sent a copy of the evaluation protocol along with the principal investigator’s email address. All respondents were informed of the study’s aims and participated voluntarily through a survey available in both digital format (77.3%; n = 201) and paper-and-pencil format (22.7%; n = 59). In the digital format, information was collected anonymously through an electronic survey distributed by the coordinators at each organisation over the online Survio platform. In the paper-and-pencil format, the research team visited the organisation with printed copies of the survey in response to a telephone call from the corresponding coordinator. The coordinator’s task was to facilitate the research team’s access to a network of potential participants, both by sharing the link to our Survio questionnaire and by convening meetings to complete the paper-and-pencil surveys. The study was approved by the University of the Basque Country’s Ethics Committee for Research with Humans, and the data was collected in accordance with the committee’s guidelines and the current data protection act.

3.2. Participants

Participants included unionised and non-unionised workers from the Autonomous Community of the Basque Country in Spain. The participating organisations were contacted through the ELA trade union. A total of twelve organisations participated from the industrial (63.8%) and service sectors (31.2%). Of the 263 participants in the original sample, 260 reported on the variables of interest. Of these, 55.4% were trade union members. The majority of these union members reported having belonged to their union for 5 or more years (n = 90; 34.6%), with a smaller number having been unionised for only 1–3 years (n = 28), 2–5 years (n = 19), or 1 year or less (n = 13). Of the sample of 144 union members, 43.5% were aged between 41 and 50 years, 31.4 were aged between 20 and 40 years, and 21.3% between 51 and 60 years. Just over half (53.7%) were women (44.4% were men; 1.9% were non-binary). Regarding non-unionised workers, 46.5% were aged between 41 and 50 years, followed by 33.8% between 51 and 60 years, 12% between 31 and 40 years, 4.9% between 20 and 30 years, and 2.8% more than 60 years; 51% were women (48.3% men; 0.7% non-binary).

3.3. Instruments

Psychological well-being was assessed using the Spanish version of the Psychological Well-Being Scales (Ryff 1989) adapted by Díaz et al. (2006). These scales comprise 29 items ranging from 1 = “strongly disagree” to 6 = “strongly agree”: 4 items regarding self-acceptance, 5 items regarding positive relations, 6 items regarding autonomy, 5 items regarding environmental mastery, 4 items regarding personal growth, and 5 items regarding purpose in life. Cronbach’s alpha was acceptable for all six dimensions: 0.83 for self-acceptance; 0.80 for positive relations; 0.70 for autonomy; 0.65 for environmental mastery; 0.77 for personal growth; and 0.87 for purpose in life.

To measure job satisfaction, we used the Generic Job Satisfaction Scale (MacDonald and MacIntyre 1997), which is considered a parsimonious and reliable instrument. Compared to other general scales, which range from 50 to 100 items (Smith et al. 1969; Weiss et al. 1967), this scale provides valid and reliable scores with only 10 items and has been localized into several different languages. In this study, we used the Spanish version, which was adapted and validated by Salessi and Omar (2006) and contains 7 items (α = 0.79), ranging from 1 = “never” to 5 = “always”.

The Life Satisfaction Scale by Diener et al. (1985) was used to measure life satisfaction. The ease with which this instrument can be administered and interpreted has led to it being validated and used in a range of different cultures and languages. For the purposes of the present study, we used the 5-item Spanish adaptation by Pons et al. (2002) (α = 0.88), ranging from 1 = “strongly disagree” to 7 = “strongly agree”.

Trade union membership was assessed by asking participants whether or not they belonged to a trade union (1 = yes; 0 = no). Finally, sociodemographic data were gathered, including age, gender, and the sector in which respondents were employed.

4. Results

Table 1. Correlations between the study variables.

	1	2	3	4	5	6	7	8	9	10	11
1. Member	1
2. Gender (woman)	−0.026	1
3. Age (>41 years)	0.17 **	0.10	1
4. Self-Acceptance	0.077	−0.019	0.087	1
5. Positive Relations	0.084	0.103	−0.025	0.473 **	1
6. Autonomy	0.191 **	−0.067	0.064	0.553 **	0.412 **	1
7. Environmental Mastery	0.137 *	0.046	0.082	0.721 **	0.559 **	0.532 **	1
8. Personal Growth	0.129 *	0.229 **	−0.048	0.550 **	0.495 **	0.357 **	0.533 **	1
9. Purpose in Life	0.042	0.040	0.073	0.765 **	0.460 **	0.449 **	0.755 **	0.581 **	1
10. Job Satisfaction	−0.191 **	0.005	0.003	0.259 **	0.242 **	0.145 *	0.284 **	0.108	0.287 **	1
11. Life Satisfaction	0.002	0.052	0.037	0.696 **	0.438 **	0.358 **	0.594 **	0.390 **	0.659 **	0.472 **	1

Note. p * < 0.01; ** p < 0.001.

presents bivariate correlations. Being a member of a trade union was associated with higher scores for autonomy, environmental mastery, and personal growth, although it was also associated negatively with job satisfaction. Positive and significant correlations were found between all variables (the six dimensions of well-being, job satisfaction, and life satisfaction). In addition, gender (being a woman) was particularly highly correlated with personal growth, and age (older than 41) to being a union member.

Chi-square tests with continuity correction were carried out in order to compare the distribution of gender (woman = 1; man = 0) and age (1 = 41 years or more; 0 = 41 years or less) across the two groups of unionized and non-unionized workers (unionized = 1; non-unionized = 0). Results indicated non-significant relationships between gender and being a union member. However, in relation to age, significant relationships were found χ² (1, 251) = 6.523, p < 0.05).

A two-sample t-test was conducted to analyse differences between trade union members and non-members in self-acceptance, positive relations, autonomy, environmental mastery, personal growth, purpose in life, job satisfaction, and life satisfaction (see

Table 2. Descriptive statistics and mean differences between trade union members and non-members in relation to psychological well-being, job satisfaction, and life satisfaction.

	Members		Non-Members		t	p
	M	(SD)	M	(SD)
Well-being: Self-acceptance	4.66	0.91	4.51	0.91	1.23	0.220
Well-being: Positive Relations	4.83	0.92	4.66	1.04	1.33	0.184
Well-being: Autonomy	4.48	0.94	4.12	0.89	3.10	0.002
Well-being: Environmental Mastery	4.79	0.79	4.57	0.76	2.20	0.030
Well-being: Personal Growth	4.98	0.94	4.73	0.98	2.10	0.040
Well-being: Purpose in Life	4.63	1.02	4.55	0.95	0.67	0.503
Job Satisfaction	3.59	0.75	3.87	0.69	−3.10	0.002
Life Satisfaction	5.05	1.1	5.05	1.3	0.03	0.973

). Significant differences were found in relation to autonomy (t = 3.10; p < 0.01), environmental mastery (t = 2.20; p < 0.05), and personal growth (t = 2.10; p < 0.05), with trade union members having higher mean scores than their non-unionised counterparts. The results also revealed significant differences for job satisfaction (t = −0.31; p < 0.01), although in this case, non-unionised workers scored higher than their unionised counterparts.

5. Discussion

The aim of this study was to analyse the differences between unionised and non-unionised workers of the Basque Country in psychological well-being (i.e., self-acceptance, positive relations, autonomy, environmental mastery, purpose in life, and personal growth), job satisfaction, and life satisfaction.

The results obtained for each of the dimensions of psychological well-being suggest that unionised workers have higher levels of autonomy, environmental mastery, and personal growth. This finding partially confirms our first hypothesis (H1) and is consistent with what has been reported to date in the existing literature, suggesting that trade union membership fosters autonomy by offering workers the possibility of exercising greater control over certain aspects of their personal and family lives, thereby enhancing their independence (Carriere 2020; Lott 2014; Rosenberg 2009). In this regard, it should be noted that the process of self-selection itself (Bardi et al. 2014), whereby individuals choose unions based on their objectives and values, contributes to improving levels of autonomy, given that self-selection is a practical way to exercise autonomy, making individuals feel more in control. Likewise, the result obtained for environmental mastery is consistent with the idea that trade union activity and collective action generate a feeling of empowerment (by giving a ‘voice’ to minorities and increasing their ability to right wrongs), which in turn results in a greater sense of control over the work environment and greater job security (Bada et al. 2018; Becker et al. 2024; Kirton 2017; Mann 2011; Sweetman 2018). The positive association found for personal growth supports the role played by trade unions in improving their members’ communication, social, and problem-solving skills, thereby helping them reach their full potential (Becker et al. 2024; Radcliff 2005). Our results suggest that this is something particularly appreciated by women who might likely be more concerned than men with the specific issue of personal growth, as recent research has pointed out (Brown et al. 2025). In contrast, no significant differences were found between unionised and non-unionised workers in terms of self-acceptance, positive relations, or purpose in life. Although the (limited) existing literature posits that trade union membership should indeed promote self-acceptance (through improved self-esteem) (Carriere 2020; Fuller and Hester 2001; Hagedorn et al. 2016; Lott 2014; Rosenberg 2009), positive relations (by fostering a sense of community and strengthening social support networks) (Becker et al. 2024; Hagedorn et al. 2016; Lott 2014), and purpose in life (by enabling members to set themselves and achieve positive goals) (Lott 2014; Mann 2011; Pacek 2009), these effects were not found to be significant in our sample. However, given that, to the best of our knowledge, this is the first time that Ryff’s ‘Multidimensional Model of Psychological Well-being’ (Ryff 1989) has been applied to the study of trade union membership (as noted in the Introduction), it would be advisable to replicate this study in larger samples. Furthermore, it would be useful to consider the effect of different mediating variables (such as members’ level of commitment to their trade union) on possible associations between trade union membership and psychological well-being.

Significant differences were found between unionised and non-unionised workers in terms of job satisfaction. However, contrary to expectations, non-unionised workers scored significantly higher in this variable than their unionised counterparts. Therefore, the second hypothesis (H2) is rejected. This finding is inconsistent with much of the empirical evidence indicating the positive contribution made by trade union membership to job satisfaction (Peetz 2012; Flavin and Shufeldt 2016; Chawla et al. 2018; Blanchflower et al. 2021). However, it is consistent with both the ongoing debate and the reverse causality hypothesis (Laroche 2016), according to which dissatisfied workers are more likely to join trade unions than their satisfied counterparts as a means of improving their unsatisfactory working conditions. Along the same lines, the Attraction/Attention/Restraint theory (ASA, Schneider et al. 1995) argues that similar people tend to group together in spaces that match their goals and values, becoming even more similar through this process of socialisation.

In relation to life satisfaction, no significant differences were found between unionised and non-unionised workers, a finding that also fails to confirm part of our third hypothesis (H3). Although most of the (few) studies that have been carried out in this field conclude that belonging to a trade union has a positive effect on workers’ life satisfaction (Charman and Owen 2014; Flavin et al. 2010; Flavin and Shufeldt 2016; Lee 2022), our finding adds to the discrepancies observed previously in the literature regarding this difference, as some studies have found no significant differences between unionised and non-unionised workers in life satisfaction while others have found negative associations between the two variables (Becker et al. 2024; Charman and Owen 2014; Lee 2022). The lack of significant differences between unionised and non-unionised workers in terms of life satisfaction may also be due to the possible mediation of other mechanisms (such as job satisfaction), which may interfere with this association.

This study is not without its limitations. The first is linked to the imbalance in the sample, given that the number of unionised workers was higher than that of non-unionised workers. The second limitation is related to the overall completion rate of the questionnaire filled in online over the Survio platform, which was only 40%. This means that six out of every ten people who accessed the questionnaire failed to complete it. Based on the feedback provided by the coordinators at the participating organisations, we can conclude that the main reason for this low completion rate was the length of the questionnaire. The third limitation is that our study was based on the assumption that being a member of a trade union necessarily entails a commitment of the members to that union. However, as indicated by the principal models of trade union commitment (Gordon et al. 1980; Sverke and Kuruvilla 1995; Tetrick et al. 2007), this is not always the case. Future studies should strive to recruit more balanced samples, making sure to include a higher number of non-unionised workers. We also recommend reducing the length of the questionnaire so that it can be completed more quickly. Finally, it would be useful to assess the level of commitment felt by unionised workers, as scores for the three variables studied are likely to differ between committed and non-committed members, with the former perceiving greater benefits.

Despite its limitations, the present study makes a significant contribution to the existing body of literature, as it explores differences between unionised and non-unionised workers in mental health (a field of study that is as relevant as it is under-researched). Moreover, it does so in a new context (the Basque Country) using a multidimensional model of psychological well-being (Ryff 1989).