Association between depressive symptoms and employment type of Korean workers: the Fifth Korean Working Conditions Survey

Over the past few decades, there has been a marked shift from standard to nonstandard employment (NSE) [1]. NSE is a grouping of different employment arrangements that deviate from the standard employment type, including temporary employment, part-time work, temporary agency work, other multi-party employment relationships, disguised employment relationships, and dependent self-employment. Another factor, precarious work, accounts for a considerable portion of NSE. While, to date, no internationally unified standard to define precarious work exists, it is broadly defined as workers who experience instability, lack of labor protection, insecurity, and social and/or economic vulnerability [2]. In Korea, it can be divided into non-permanent workers, part-time workers, and non-typical workers [3]. Companies in Korea have been actively using precarious workers because the labor market flexibility helps them reduce costs and manage manpower flexibly [4]. Previous study suggested that women and older people are more likely to be precarious worker [5]. Many women voluntarily resign or change to precarious jobs because of gender roles related to marriage or having children [6]. The proportion of precarious workers among all workers in Korea in 2022 will be 27.3%, the second highest among Organization for Economic Cooperation and Development (OECD) countries after the Netherlands (27.7%) [7].

Precarious work can be related to socioeconomic factors such as income, education level, marital status, job type, or social protection [6, 8]. Socioeconomic factors were identified as confounding factors in previous studies that analyzed precarious workers and depressive symptoms. In addition, several studies have reported that job stress is a harmful factor that increases the risk of depression [9‐12]. To analyze the relationship between employment type and depressive symptoms, it is necessary to analyze job stress and socioeconomic status factors as well.

Mental disorders are one of the leading causes of global health-related burden, with depressive and anxiety disorders ranked among the top 25 [13, 14], according to the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019.

It is important to identify and manage workers’ depressive symptoms, as the prevalence of such symptoms can impair their work [15]. One study evaluated an Employee Assistance Program and reported an 86% reduction in suicide risk among Japanese workers with preexisting suicidal thoughts [16]. These findings indicate the need for interventions to manage workers’ mental health problems such as depression.

To identify the relationship between precarious work and depressive symptoms, prospective data from the U.S. National Longitudinal Survey of Youth 1979 (NLSY79) of American men and women between 14 and 22 years of age in 1979 revealed that those who had been exposed to precarious work in the two years preceding the outcome measurement were at risk [17]. A study using the fifth Korea National Health and Nutrition Examination Survey data reported that precarious work was associated with depressive symptoms and suicidal ideation [18]. The Korean Welfare Panel Study indicated that employment status changes, from permanent to precarious work, were associated with the onset of depressive symptoms [6, 19]. Precarious work appeared to be associated with depressive symptoms after adjusting for socioeconomic factors; however, the evidence might be insufficient because the study subjects were relatively small and did not target workers.

We used data from The Korean Working Conditions Survey (KWCS) to evaluate the association between precarious work and depressive symptoms. The KWCS is one of the most representative surveys of Korean workers, with systematic and representative sampling of the Korean working population [20]. In this survey, depressive symptoms were investigated using the World Health Organization (WHO)-5 Well-Being Index. Although this index was designed as a tool to assess the quality of life and mood, it has sufficient validity as a screening tool for depressive symptoms as well and has been successfully applied in a wide range of research fields [21, 22]. However, studies using objective indicators such as the WHO-5 Well-Being Index on the association between precarious workers and depressive symptoms in a representative group in Korea are rare [6].

Therefore, this study aimed to analyze the association between depressive symptoms and the employment type of workers, considering both socioeconomic status and job stress factors, using an objective method with representative data from Korean workers.

This study evaluated the association between depressive symptoms and employment type in Korean workers using the fifth KWCS. In this study, the unweighted frequencies (%) of depressive symptoms were 33.43% for regular workers and 44.29% for precarious workers (p < 0.001) (Table 3). The frequency of depressive symptoms was 42.50% in precarious workers and 32.54% in regular workers (p < 0.001). The prevalence of depressive symptoms was relatively higher than that reported in the previous study, in which depressive mood was reported to be 13.1% for precarious workers and 7.8% for regular workers [16]. This might be due to the difference in the definition of precarious workers, as well as the assessment method for diagnosis of depressive symptoms.

Crude and multivariate analyses showed that precarious workers had significantly increased depressive symptoms compared with regular workers (all p < 0.001, Table 4). The precarious workers had significantly higher risks of depression than regular workers after adjusting weights and other variables (OR 1.16; 95% CI 1.07–1.16). After PSM adjustment, the significant association between depressive symptoms and precarious workers remained in both crude and multivariate analyses (Table 5). In a Korean cross-sectional study, the adjusted OR for depressive symptoms in precarious workers was 1.32 [18]. Another recent study on the Korean population suggested the independent effects of precarious work on depression after controlling for confounding factors [6]. One study showed that the transition from full-time permanent employment to another employment status is associated with the development of severe depressive symptoms [8]. A study using nationally representative data from the United States also found that exposure to precarious work was associated with increased depressive symptom severity [17]. A study using nationally representative data from Chile also showed that precarious work was associated with anxiety and depression after controlling for age, sex, and occupational group [27]. A Swedish study suggested that precarious employment is a risk factor for poor mental health among young individuals [28]. The independent effects of precarious work on poor mental health status have been consistently suggested in previous studies, and with regard to the mechanism of this association, the possible influence of psychological stress induced by job insecurity or disadvantaged job conditions on workers’ mental health has been suggested [29]. As an explanation for the association, people with poor mental health in the early stages of life are more likely to have precarious work, as their mental health problems can potentially reduce their chances of obtaining a quality job [30]. Depressive symptoms and job instability may have a vicious cycle.

We found that socioeconomic factors, such as age, gender, education, income, and current health status were associated with both precarious work and depressive symptoms in adult workers (Supplementary Table S1). In this study, the adjusted OR for depressive symptoms of women was 0.91 (95% CI 0.84–0.98). This was consistent with a previous study of Japanese workers in which the relationship between precarious work and severe psychological distress was significant only for male workers in the adjusted model [29]. A previous study also indicated that employment changes from regular to precarious work were associated with the onset of new depressive symptoms for the families’ main earners [8]. Our results are explained by the fact that the most common earners in a Japanese or South Korean worker’s family are likely to be men. We also find that lack of job satisfaction and support from colleagues affected depressive symptoms (OR 1.27, 95% CI 1.09–1.47; OR 1.67, 95% CI 1.55–1.80). Job satisfaction is associated with the incidence of burnout symptoms at work and can affect depressive symptoms [31]. Moreover, one study found that low control over worktime was associated with increased depression/anxiety scores (relative risk [RR] 1.61, 95% confidence interval [CI] 1.39–1.87) [27]. These results demonstrate the need for job stress interventions in the workplace.

This study had some limitations. First, it was a cross-sectional study. Although precarious work and depressive symptoms are related, it is not possible to establish a causality between the two. Longitudinal studies, such as cohort studies, may be helpful for this purpose. Second, factors related to depressive symptoms, which may include a person’s history of psychological diseases such as major depressive disorder and anxiety disorder, were not considered. We attempted to compensate for this limitation by adding a self-rated health item to our questionnaire. In addition, although smoking and alcohol consumption might be linked to depressive symptoms [32], the fifth KWCS does not survey these factors. Smoking and alcohol consumption were investigated by up to the fourth KWCS; however, due to the inaccurate responses in the self-reported questionnaire, these were excluded from fifth KWCS. Therefore, unfortunately, we were unable to adjust for smoking and alcohol consumption in this study. As such, a more accurate assessment of smoking and alcohol consumption in future surveys may help assess the risk of workers developing symptoms of depression.

Third, only workers currently employed at the time of the survey were included in the KWCS. Workers who already had severe depression, took a break from work, or quit treatment completely were excluded.

Despite these limitations, this study analyzed depressive symptoms according to one’s employment type using a questionnaire and representative data from Korean workers by applying weights and analyzing socioeconomic and job stress factors. Future research should analyze various occupational characteristics, such as industry classification, subtype of precarious work, and work type according to the WHO-5 Well-Being Index. These studies may provide important basic data for preventing and managing depression among workers.