In the past few decades, changes in industrial structure and economic crises have led to an increase in the proportion of employment contracts other than standard employment.Reference Cooke and Jiang1 These non-standard types of employment contracts comprise temporary employment, part-time employment, disguised employment and employment arrangement via digital platforms.2 In particular, the informalisation of employment was accelerated by the recent COVID-19 pandemic. The COVID-19 pandemic caused an economic crisis and brought changes to the industrial structure, resulting in companies increasing their proportion of non-standard employment.Reference Fana, Torrejón Pérez and Fernández-Macías3
Temporary employment
Temporary employment is widely known for its negative effects on workers’ health. For example, workers with temporary employment are at risk of fatal occupational injuriesReference Villanueva and Garcia4 and musculoskeletal problems.Reference Roquelaure, LeManach, Ha, Poisnel, Bodin and Descatja5 So far, several studies have investigated the effects of temporary employment on workers' mental health. Temporary employment can cause mental health problems because of the resulting subjective job insecurity for workers.Reference Ronnblad, Gronholm, Jonsson, Koranyi, Orellana and Kreshpaj6 Previous studies found that temporary employment is associated with psychiatric distress and depression.Reference Hammarstrom, Virtanen and Janlert7,Reference Yoo, Park, Jang, Kwon, Kim and Cho8 Kim et al reported that daily labourers had a higher risk of depressive symptoms compared with fixed-term or permanent workers in Korea.Reference Kim, Kim, Lee, Ju, Chun and Park9 Furthermore, one previous study argued that temporary employment is associated with a higher risk of suicidal ideation.Reference Sasaki, Tabuchi, Okubo, Ishimaru, Kataoka and Nishi10 However, only a few studies have examined the relationship between temporary employment and risky health behaviours such as alcohol consumption. Although some researchers maintained that temporary employment was associated with alcohol misuseReference Park, Lee and Lee11 and increased mortality owing to alcohol-related diseases,Reference Kivimaki, Vahtera, Virtanen, Elovainio, Pentti and Ferrie12 others found no significant relationship between alcohol use and temporary employment.Reference Park, Kim, Lee and Park13
Job dissatisfaction
Along with temporary employment, job satisfaction is also a major determinant of workers’ mental health. Job dissatisfaction is a well-known cause of burnoutReference Oliveira, Silva, Galvao and Lopes14 and reduced well-beingReference Bowling, Eschleman and Wang15 of workers. Previous longitudinal and meta-analytic studies have reported that decreased job satisfaction is closely related to the poor mental health of workers.Reference Faragher, Cass and Cooper16,Reference Dirlam and Zheng17 For example, cumulative years of job dissatisfaction were found to be associated with depressive symptomsReference Oshio18 and anxiety.Reference Saquib, Zaghloul, Saquib, Alhomaidan, Al-Mohaimeed and Al-Mazrou19 On the other hand, the effect of job dissatisfaction on alcohol use is not unknown. Although one cross-sectional study found an association between job dissatisfaction and alcohol misuse among young male workers,Reference Legleye, Baumann, Peretti-Watel, Beck and Chau20 another study found that job dissatisfaction did not mediate the relationship between work stress and alcohol use disorder.Reference Berger, Sedivy, Cisler and Dilley21
Association of temporary employment and job dissatisfaction with mental health problems
Recently, there has been growing social interest in protecting workers’ mental health. Alcohol use disorder and depression are major causes of suicidal thoughts/behaviour, and can induce various physical illnesses such as liver diseases and obesity.Reference Jantaratnotai, Mosikanon, Lee and McIntyre22 Impaired mental health is harmful not only to workers themselves, but also to their organisations, as problematic alcohol consumption and depression negatively affect an individual's work performance.Reference Thorrisen, Bonsaksen, Hashemi, Kjeken, van Mechelen and Aas23,Reference Lerner, Adler, Rogers, Chang, Lapitsky and McLaughlin24
Currently, there are no studies that focus on the importance of job satisfaction for mental health problems in the context of temporary employment. In general, temporary employment has been reported to be closely correlated with low job dissatisfaction.Reference Aleksynska25 Nevertheless, the relationship between temporary employment and job satisfaction depends on the characteristics of the worker. For instance, a decrease in job satisfaction was observed only in individuals who worked involuntarily in temporary employment, and in the case of voluntary temporary workers, no significant relationship between employment type and job satisfaction was found.Reference Park and Kang26 Also, an interactional analysis by Hammarström et al. found that the health effect of temporary employment varied according to individual characteristics, such as education level.Reference Hammarstrom, Virtanen and Janlert7 Thus, it could be hypothesised that the impact of temporary employment on the mental health of workers could be moderated by job satisfaction. Consequently, identifying how temporary employment and job dissatisfaction interact would provide new insight into the effect of temporary employment on workers’ mental health.
To sum up, the effect of temporary employment and job dissatisfaction on alcohol use disorder has not yet been identified. In addition, to the best of our knowledge, the combined effect of temporary employment and job dissatisfaction has not yet been reported. Therefore, our study will contribute to the literature by exploring the association of temporary employment and job dissatisfaction with alcohol use disorder and depressive symptoms, using a longitudinal data-set consisting of a nationally representative study sample. Finally, we aimed to discover social determinants affecting workers’ mental health, and provide evidence that could be used for policy development.
Method
Study sample
This study used the Korea Welfare Panel Study (KoWePS) data-set. The KoWePS is an ongoing annual panel survey conducted by the Seoul National University Social Welfare Research Centre and the Korea Institute for Health and Affairs since 2006. To collect nationally representative households in Korea, the KoWePS used two-stage stratified cluster sampling based on the South Korea Population and Housing Census. In this sampling method, the census enumeration district was employed as the primary sampling unit, and the household was employed as the secondary unit. The survey was conducted by trained interviewers using one-on-one computer-assisted personal interviews.
As the questionnaire regarding alcohol use disorder was introduced in 2009, study participants from 2009 to 2021 were included in this study. Out of a total of 23 692 participants with 204 336 observations, we limited our sample to those aged between 19 and 64 years because 65 years is the retirement age in Korea, leaving 14 703 participants with 107 591 observations. Next, we limited our sample to employed workers, leaving 9922 participants with 55 770 observations. After excluding 3131 observations with missing values, our final sample included 9611 participants with 52 639 observations.
Ethics statement
The Institutional Review Board (IRB) of Yonsei Health System approved this study (approval number: 4-2022-0793). The requirement of informed consent was waived by the IRB because of the retrospective nature of this study.
Main variables
Employment type
Employment types were classified as permanent workers, fixed-term workers and daily labourers. Permanent workers were employees who worked under a labour contract period of ≥1 year. Fixed-term workers were employees who worked under a labour contract period of ≥1 month to <1 year. Daily labourers were employees with a labour contract period of <1 month or those who were paid daily.
Job satisfaction
Job satisfaction was measured on a five-point Likert scale (1 = ‘very dissatisfied’, 2 = ‘fairly dissatisfied’, 3 = ‘neither satisfied nor dissatisfied’, 4 = ‘fairly satisfied’ and 5 = ‘very satisfied’). We then classified workers’ job satisfaction as ‘dissatisfied’ (fairly dissatisfied or very dissatisfied), ‘neutral’ (neither satisfied nor dissatisfied) or ‘satisfied’ (fairly satisfied or very satisfied).
Alcohol use disorder
The Alcohol Use Disorders Identification Test (AUDIT) was used to classify alcohol use disorders in this study. The ten-item AUDIT developed by the World Health OrganizationReference Babor, Higgins-Biddle, Saunders and Monteiro27 is a validated screening tool for identifying individuals with alcohol use disorder and has been widely used in epidemiologic studies. Each question is measured on a five-point Likert scale ranging from 0 to 4, so the total scores ranged from 0 to 40. According to previous studies, those with a score of ≥16 were considered to have a high level of alcohol problems and required clinical intervention and monitoring.Reference Babor, Higgins-Biddle, Saunders and Monteiro27 Thus, the same value was used in this study for classifying those who had alcohol use disorder.
Depressive symptoms
Depressive symptoms were measured with the 11-item Centre for Epidemiologic Studies Depression Scale (CESD-11), a short version of the original 20-item CESD. The validity of the CESD-11 was confirmed in a previous Korean study.Reference Lee28 Each question was measured with a four-point Likert scale ranging from 0 to 3, so that the sum of the scores ranged from 0 to 33. The total score was multiplied by 20 and then divided by 11. We defined those with a score of ≥16 as having depressive symptoms, because the cut-off value of the 20-item CESD is 16.Reference Vilagut, Forero, Barbaglia and Alonso29
Covariates
Gender, age, household income, education, marital status, occupation, weekly working hours, workplace size and survey year were considered as the confounders in our study. The age groups were classified as <30, 30–39, 40–49, 50–59 and ≥60 years. Household income was classified into quartiles (Q1–Q4). Education level was classified as having completed college, high school or below. Chronic disease status was classified as having at least one chronic disease being treated or taking medication or not. Smoking status was classified as current smokers or past/non-smokers. Marital status was classified as married, unmarried or other (divorced, widowed or separated). Occupation was classified as blue collar, service and sales worker, and white collar, according to the Korean Standard Classification of Occupations. The Korean Standard Classification of Occupations classifies managers, professionals and clerks as white-collar workers. Service workers and sales workers are classified as service and sales workers. Also, agricultural, forestry and fishery workers; craft and related trades workers; plant workers, machine operators and assemblers; and elementary workers are classified as blue-collar workers. Weekly working hours were classified as ≤40 or >40 h. According to the number of employees in the respondent's organisation, workplace size was classified as <30 workers, 30–99 workers or ≥100 workers. In addition, we also considered wave-specific effects by including binary dummy variables for each survey year in the fully adjusted models.
Statistical analysis
For descriptive analysis, the χ 2-test was used to compare the prevalence of alcohol use disorder and depressive symptoms according to the socioeconomic features of the study participants. For regression analysis, we initially performed pooled cross-sectional logistic regression and a generalised linear mixed model with a logit link in the next step to estimate the odds ratios and 95% confidence intervals. Models with random intercepts by individuals were used in the mixed-model analysis to analyse the repeatedly measured survey data. For model comparison, log likelihood and Akaike information criterion (AIC) values were calculated. For individual i and year t, the model specification is as follows:
where Y denotes mental health outcomes (alcohol use disorder and depressive symptoms), E1 and E2 denote employment type (fixed-term workers and daily workers), S1 and S2 denote job satisfaction (neutral and dissatisfied), ui denotes participant-specific effect and ɛit denotes the error. Also, to clarify the temporal association, we explored how the changes in employment status and job satisfaction affect mental health outcomes by applying a 1-year lag time to each independent variable.
For measuring the combined effect of temporary employment and job dissatisfaction, the two variables were grouped and newly classified into nine groups, ‘employment type (permanent worker) + job satisfaction (satisfied)’ to ‘employment type (daily labourer) + job satisfaction (dissatisfied)’. The relative excess risk due to interaction (RERI) was calculated to assess the supra-additive interaction between temporary employment and job dissatisfaction. We estimated the RERI by using the following equation:
The 95% confidence interval of RERI was calculated by using the delta method.Reference Hosmer and Lemeshow30 A RERI of >0 suggests supra-additive (synergistic) interaction between two variables. A P-value of <0.05 was considered statistically significant, and P-values were two-tailed. All statistical analyses were performed with R for Windows (version 4.2.1; R Foundation for Statistical Computing, Vienna, Austria; https://www.r-project.org). The R package glmmTMB was used to fit generalised linear mixed models.
Results
Table 1 shows the socioeconomic features of the study participants based on pooled observations. Among the total observations, 29.7% and 13.5% were fixed-term workers and daily labourers, respectively. The highest prevalence of alcohol use disorder was observed among daily labourers (7.6%), followed by permanent workers (6.1%) and fixed-term workers (3.9%). The prevalence of depressive symptoms was 4.6% for permanent workers, 8.3% for fixed-term workers and 14.0% for daily labourers. Moreover, among those who were dissatisfied with their jobs, 8.7% and 18.2% of the workers had alcohol use disorder and depressive symptoms.
Table 2 shows the association between temporary employment and job dissatisfaction, and alcohol use disorder. The fully adjusted generalised linear mixed model showed the best model fit (log likelihood and AIC). In the fully adjusted generalised linear mixed model, employment type and job satisfaction were associated with alcohol use disorder. Fixed-term workers did not show a significantly higher risk for alcohol use disorder (odds ratio 1.11, 95% CI 0.94–1.30) compared with permanent workers; however, being a daily labourer was associated with alcohol use disorder (odds ratio 1.54, 95% CI 1.22–1.95). Regarding job satisfaction, those who were neither satisfied nor dissatisfied (odds ratio 1.33, 95% CI 1.18–1.50) or were dissatisfied (odds ratio 1.78, 95% CI 1.52–2.08) with their jobs were associated with an increased risk for alcohol use disorder compared with those who were satisfied.
Table 3 shows the association between temporary employment and job dissatisfaction, and depressive symptoms. The fully adjusted generalised linear mixed model has the best model fit (log likelihood and AIC). In the generalised mixed model, employment type and job satisfaction were associated with depressive symptoms. Being a fixed-term worker (odds ratio 1.12, 95% CI 1.00–1.26) or daily labourer (odds ratio 1.68, 95% CI 1.44–1.95) was associated with depressive symptoms compared with permanent workers. Additionally, those who were neither satisfied nor dissatisfied (odds ratio 2.44, 95% CI 2.22–2.69) or were dissatisfied (odds ratio 4.88, 95% CI 4.36–5.46) with their jobs were associated with an increased risk for depressive symptoms.
Figures 1 and 2 show the combined effect of temporary employment and job dissatisfaction on alcohol use disorder and depressive symptoms. This effect became stronger for those who were concurrently exposed to temporary employment and job dissatisfaction. For instance, daily labourers who were dissatisfied with their jobs showed the highest risk for alcohol use disorder (odds ratio 2.99, 95% CI 2.21–4.03) and depressive symptoms (odds ratio 9.00, 95% CI 7.36–11.02). The RERI was estimated to assess the additive interaction between temporary employment and job dissatisfaction. The RERI for fixed-term employment and job dissatisfaction was 0.36 (95% CI −0.26 to 0.99; P = 0.259) for alcohol use disorder and 0.37 (95% CI −0.69 to 1.42; P = 0.508) for depressive symptoms. The RERI for daily employment and job dissatisfaction was 0.91 (95% CI 0.06–1.76; P = 0.036) for alcohol use disorder and 3.47 (95% CI 1.80–5.14; P < 0.001) for depressive symptoms, suggesting a supra-additive interaction between the two variables.
Finally, Table 4 presents the effect of the sequential experience of employment status and job satisfaction (previous year → concerned year) on outcomes. The results show that the shift to daily employment (permanent/fixed-term → daily employment) and the retention of daily employment for two consecutive years (daily → daily employment) are significantly related to alcohol use disorders and depressive symptoms. In addition, deterioration of job satisfaction (satisfied/neutral → dissatisfied) and experience of job dissatisfaction for two consecutive years (dissatisfied → dissatisfied) are also related to alcohol use disorders and depressive symptoms.
Discussion
Our study provides evidence of the detrimental health effects of temporary employment and job dissatisfaction. We investigated the effects of temporary employment and job dissatisfaction on alcohol use disorder and depressive symptoms. We confirmed that temporary employment and job dissatisfaction were associated with an increased risk of alcohol use disorder and depressive symptoms. Furthermore, our study suggests that the effects became stronger when temporary employment and job dissatisfaction were combined. In addition, the RERIs between daily employment and job dissatisfaction were >0 for alcohol use disorder and depressive symptoms, indicating a supra-additive (synergistic) interaction between the two variables.
Our findings are consistent with previous research showing that insecure employment is associated with alcohol use disorderReference De Cuyper, Kiran, De Witte and Aygoğlu31,Reference Marchand, Parent-Lamarche and Blanc32 and depressive symptoms,Reference Kim, Kim, Lee, Ju, Chun and Park9,Reference Kim, Muntaner, Khang, Paek and Cho33 but contradict the finding that there is no significant association between temporary employment and alcohol use disorder.Reference Park, Kim, Lee and Park13 Although fixed-term employment was not associated with alcohol use disorder, daily labour was significantly associated with an increased risk of alcohol problems than permanent employment. In addition, daily labourers had higher odds ratios for alcohol use disorder and depressive symptoms compared with fixed-term workers, suggesting that a shorter duration of an employment contract is associated with an increased risk for mental health problems.
Along with temporary employment, our study also found that job dissatisfaction was significantly associated with alcohol use disorder and depressive symptoms. Our results support the findings from previous studies that alcohol use disorder and depressive symptoms are affected by workers’ job satisfaction.Reference Oshio18–Reference Legleye, Baumann, Peretti-Watel, Beck and Chau20 Additionally, the more that workers became dissatisfied with their job, the stronger the effect. For example, those who were dissatisfied with their job had higher odds ratios than those who were neither satisfied nor dissatisfied.
To the best of our knowledge, our study is the first to suggest that workers show greater risks for alcohol use disorder and depressive symptoms when they are simultaneously exposed to temporary employment and job dissatisfaction. According to previous studies, the job demand–control modelReference Karasek34 and the effort–reward imbalance modelReference van Vegchel, de Jonge, Bosma and Schaufeli35 explain workers’ stress. Job dissatisfaction reflects imbalances between job demand and controlReference Rodríguez, Bravo, Peiró and Schaufeli36 and job effort and reward.Reference Li, Yang, Cheng, Siegrist and Cho37 Additionally, insecure employment reduces workers’ perceived rewards, causing an imbalance between effort and reward.Reference de Jonge, Bosma, Peter and Siegrist38 Thus, temporary employment and job dissatisfaction are more stressful when they are combined. Moreover, the combined effect of temporary employment and job dissatisfaction was greater than their sum.
Earlier studies have tried to identify the possible mechanisms by which temporary employment and job dissatisfaction affect workers’ mental health.Reference Tatsuse and Sekine39,Reference Park and Iacocca40 The detrimental effect of temporary employment and job dissatisfaction on mental health problems could be explained by elevated work stress among employees. Employment insecurity and job dissatisfaction increase work-related stressReference De Sio, Cedrone, Trovato Battagliola, Buomprisco, Perri and Greco41 and anxietyReference Saquib, Zaghloul, Saquib, Alhomaidan, Al-Mohaimeed and Al-Mazrou19 among workers, which in turn, increases the risk for mental health problems. One previous study revealed that stress-related mental health problems could be induced by job dissatisfaction.Reference Tatsuse and Sekine39 Similarly, Tatsuse et al found that lack of job satisfaction significantly predicted depression.Reference Tatsuse, Sekine and Yamada42 Moreover, to cope with work stress triggered by job insecurity and dissatisfaction, employees may turn to risky health-related behaviours such as cigarette smoking, substance misuse and alcohol misuse.Reference Park and Iacocca40 For example, stressful psychosocial work environment such as effort–reward imbalance can act as a trigger for heavy alcohol consumption.Reference Head, Stansfeld and Siegrist43
Physiological mechanisms also explain the relationship between temporary employment and job dissatisfaction, and mental health problems. According to previous studies, work stress and accumulated insecure employment induce dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis.Reference Gustafsson, Janlert, Virtanen and Hammarstrom44,Reference Chandola, Heraclides and Kumari45 Overactivation of the HPA axis is closely related to heavy alcohol consumptionReference Thayer, Hall, Sollers and Fischer46 and major depression.Reference Pariante and Lightman47 Thus, dysregulation of the HPA axis may mediate the relationship between temporary employment and job dissatisfaction, and alcohol use disorder and depressive symptoms. Further in-depth studies are needed to elucidate the exact mechanism of the effects of temporary employment and job dissatisfaction on workers’ mental health.
Our study has some limitations. First, the KoWePS questionnaire regarding job dissatisfaction measured workers’ overall job satisfaction. Thus, detailed aspects of the work environment, such as job demand and control, hazardous physical and psychological threats, and perceived insecurities, could not be identified in this study because of a lack of information. Second, as health outcomes in our study were self-reported, social desirability bias and recall bias should be considered. One previous study reported that survey respondents tended to underreport their alcohol consumption.Reference Davis, Thake and Vilhena48 Thus, there is a possibility that the overall prevalence of alcohol use disorder might be underestimated in this study. Third, although we employed a generalised linear mixed model to investigate the association between job characteristics and mental health problems, the possibility of reverse causality should be explored in future studies. For example, the mental health problems of workers could negatively affect their employment statusReference Evans-Lacko, Knapp, McCrone, Thornicroft and Mojtabai49 and job satisfaction.Reference Oshio18
Despite these limitations, our study has several strengths. First, we used mixed models adjusted for the personal traits of the survey participants. Personal traits can confound the relationship between job satisfaction and mental health problems. For example, workers with high levels of neuroticism have been known to report more job dissatisfaction and mental health problems.Reference Rukh, Dang, Olivo, Ciuculete, Rask-Andersen and Schioth50 From this perspective, our study overcame the limitations of previous cross-sectional studies. Next, the KoWePS study participants were selected through a systemic sampling method; therefore, the participants represented households in Korea. Thus, our study has strength in terms of its generalisability.
In summary, our current study found that temporary employment and job dissatisfaction have detrimental effects on alcohol use disorder and depressive symptoms. These effects became stronger when temporary employment and job dissatisfaction were combined. Policy makers should implement appropriate actions to ease job insecurity among temporarily employed workers, and to improve job satisfaction.
Data availability
The raw Korea Welfare Panel Study (KoWePS) data are available online (https://www.KoWePS.re.kr:442/main.do). The raw KoWePS data do not comprise personal information.
Acknowledgements
The authors would like to thank the Seoul National University Social Welfare Research Centre and the Korea Institute for Health and Affairs for sharing the raw Korea Welfare Panel Study data, and the study participants in this survey. The paper's contents are the responsibility of the authors and do not represent the official views of the Seoul National University Social Welfare Research Centre or the Korea Institute for Health and Affairs.
Author contributions
S.-U.B. conceptualised the study, was responsible for the study methodology, conducted the formal analysis and data visualisation, and wrote the original draft of the manuscript. J.-U.W. conceptualised the study, supervised the study, and reviewed and edited the manuscript. J.-H.Y. supervised the study, and reviewed and edited the manuscript.
Funding
No funding was received for this study.
Declaration of interest
None.
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