As the industrial structure of modern society evolved from its manufacturing origins, the service industry, employing a wide range of workers from highly skilled professionals to unskilled labor, is expanding rapidly. In the service sector, demand peaks are less predictable than in the manufacturing realm, and thus, staffing flexibility is a high organizational priority [1]. This required flexibility threatens standard employment relationships that guarantee full-time work with a fixed schedule and continued employment. Nonstandard employment arrangements, which include temporary employment, part-time work, temporary agency work and other forms of employment involving multiple parties, and disguised employment relationships and dependent self-employment, provide the staffing flexibility required to meet employers' needs [2]. Therefore, the use of nonstandard employment workers has steadily increased in recent years. This phenomenon is common in many developed countries, including South Korea [3]. In recent years, the number of nonstandard employment workers in that country has risen steeply, accounting for about 36.4% of all workers in August 2019[4].

An accumulating literature suggests that workers in insecure employment relationships, such as part-time and temporary workers, tend to have worse health status, including higher rates of mortality and mental health morbidity, and are at a higher risk of occupational injuries than that of workers in secure relationships, such as full-time and permanent workers [5, 6, 7]. However, most previous studies have not focused on workers in types of nonstandard employment other than part-time or temporary arrangements. Thus, there is a gap in knowledge about the health status of many nonstandard employment workers, including Korean workers in special employment relationship (WSER), the target population of this study, and whose employment quality differs in some important respects from those of part-time and temporary workers.

In Korea, WSERs are legally self-employed workers who contract with the employer individually and supply their labor in a subordinate status to the employer [8]. Therefore, their employment status is like the International Labour Organization dependent self-employed category of nonstandard employment. WSERs are not designated as or provided the protection of regular employees under the Korean Labor Standards Act [8], have few legal protections, and have substandard working arrangements in several respects. For example, although Korea's Labor Standards Act stipulates that regular wage workers (RWW) could work for 40 hours a week, the standard does not apply to WSERs. WSERs have no guarantee of break time and place and no unemployment benefit. Most WSERs are paid according to their productivity and have no guaranteed income [9]. Thus, WSERs may be exposed to long working hours because they work without breaks to maintain a certain income. Further, because much of their customer interaction takes place at customers' homes, dealing with customer problems and complaints independently, without institutional support, is an added stressor [9, 10]. Finally, few WSERs have workers' compensation insurance coverage [3] because only workers in nine of the many WSER occupations-home-visit tutor, insurance salesperson, credit card recruiter, golf game assistant, truck driver, loan collector, proxy driver, delivery person with motorcycle, and package delivery person-are legally designated as WSERs under Korea's Industrial Accident Compensation Insurance Act [11]. Thus, in multiple aspects and given evidence relating working conditions to health, WSERs may be at greater risk of poor physical and mental health outcomes than their standard employee counterparts.

Little is known about the health of WSERs, including their work-related health status, because reliable statistical data, including data on industrial accidents involving WSERs, are lacking [10, 12]. To help fill this research gap, we conducted a secondary data analysis using the 5th Korean Working Conditions Survey (KWCS) to explore the health status and determinants of health of WSERs in comparison to workers with more standard employment. We selected self-rated health (SRH) and depressive symptoms (DS) as our two dependent variables. SRH is a wellestablished valid indicator of overall health status [13, 14] and an excellent predictor of health decline and mortality [15, 16]. Workers under beneficial employment conditions and relationships, such as stable employment, regular working time, and not long working hours, have been found to have better SRH than those who do not [14, 17, 18]. Employment quality, including job insecurity and long working hours, can not only cause physical health problems but also mental health problems, including depression [19, 20].

This study aimed to compare the health status of WSERs and RWWs to examine the association between workers' employment relationships (WSER versus RWW) and selfrated health and depressive symptoms and identify factors associated with those outcomes by each group.

Table 1 shows the distributions of sociodemographic and work-related characteristics in the WSER and RWW groups. Overall, the WSERs were more likely to be female, 40 or more years old, and service and sales occupation was the most common in this group. Among the WSERs, the percentages of subjects working 53 hours or more per week, lacking a rest guarantee, having an unsuitable worklife balance, and reporting SP were higher than those of the RWWs. The unadjusted prevalence rates for fair/poor SRH were higher for WSERs at 25.2% than that for RWWs at 20.7%. DS prevalence was higher among WSERs at 28.3% than among RWWs at 25.0% (Table 1).

Table 1 Sociodemographic, Work-related Characteristics, and Health Status Click for larger image

Logistic regression analysis was performed to explore factors influencing fair/poor SRH and DS. Table 2 shows the results for the model pooling data for WSERs and RWWs, including all covariates. WSER individuals had 31% greater odds of fair/poor SRH (aOR=1.31, 95% CI=1.14~1.49) and 20% greater odds of having DS (aOR=1.20, 95% CI=1.06~1.36).

Table 2 The Difference of Adjusted Odds Ratio for Fair/poor Self-rated Health and Depressive Symptoms between WSERs and RWWs Click for larger image

Factors associated with SRH and DS among WSERs and RWWs were examined in separate models and are shown in Table 3. For fair/poor SRH, significant factors in the WSER model included age, education level, lack of a rest guarantee, and SP; these were also significant in the RWW model. The point estimates in the WSER model tended to be larger than those in the RWW model, although the wide confidence intervals for the WSER model (likely owing to the small sample size) frequently included the RWW point estimate. WSERs with low education had 4.5 times higher odds (aOR=4.53, 95% CI=2.19~9.38) of fair/poor SRH, while low-educated RWWs had just 1.5 times higher odds (aOR=1.46, 95% CI=1.22~1.73) of fair/poor SRH. In the subgroup analyses for DS, significant factors in the WSER model included occupation, enterprise size, existence of a union, average weekly work hours, lack of a rest guarantee, and SP; in the RWW model, the same factors were significant. The largest same-direction effects in the WSER and RWW models were observed for enterprise size, existence of a union, lack of a rest guarantee, and SP. However, service or sales occupation and average weekly working hours of 41~52 hours showed opposite directional effects in the two models. Specifically, among WSERs, workers with a service or sales occupation showed greater odds of DS than those having a clerical or professional occupation (aOR=1.45, 95% CI=1.06~1.98). However, among RWWs, lower odds of DS (aOR=0.86, 95% CI=0.78~0.94) were observed. In contrast, in the WSER model, workers with weekly working hours of 41~52 hours had lower odds of DS than those working 40 hours or less (aOR=0.61, 95% CI=0.45~0.83), but in the RWW model, higher odds (aOR=1.13, 95% CI=1.05~1.21) were observed.

Table 3 The results of Logistic Regression on Fair/poor Self-rated Health and Depressive Symptoms Click for larger image

This study aimed to examine the health status of WSERs and RWWs and identify the factors influencing health status in each group. We found that the WSERs reported higher poor/fair SRH (25.2%) and greater DS (28.3%) than (poor/fair SRH 20.7%, DS 25.0%) the RWWs. Despite the growing number of WSERs, their health status has received less attention in health research. Therefore, the results of this study were compared with those of previous studies that examined the associations between health status among permanent and temporary workers. For example, in analyzing KWCS data collected in 2011, Kwon et al. reported that the prevalence of poor SRH among permanent workers was 10 percentage points lower than among temporary workers, who showed an OR of 1.2 for poor SRH [24]. In addition, based on British cohort data, Emerson et al. reported the risk of fair/poor SRH among nonstandard workers to be 1.66 compared to standard workers [25]. Like our results for SRH, the mental health status of temporary/part-time workers was generally worse than that of permanent/full-time workers [6, 20, 26]. Although the temporary/part-time workers included in previous studies were not identical to WSERs in terms of work relationships, this study's results for WSERs corresponded with those of earlier studies for temporary or part-time workers.

Unlike previous studies, Julià et al. [27]'s study, which analyzed the difference in SRH and mental well-being between informal workers (similar to the WSERs of this study) and permanent workers in 27 European countries, showed no statistically significant difference in SRH or mental well-being between informal and permanent workers. Some of our study's significant results differed from those of Julià et al.[27]. In Julià et al.[27]'s study, the prevalence of poor SRH was lower, but the unadjusted prevalence of poor mental well-being was higher among informal workers than among permanent workers. In adjusted models, the authors found no statistically significant differences in SRH or mental well-being between informal and permanent workers. The authors postulated that this seemingly contradictory result may have been due to a “healthy workers bias.” Furthermore, it is possible that Korean working conditions and employment quality among WSERs may differ from those among informal workers in Europe in ways that affect health. Further research examining the influence of working environment on the health of WSERs is needed to explore this possibility.

Our study expands the knowledge of the determinants of WSERs' health. For example, we found that the likelihood of DS was very high for skilled and non-skilled manual occupations compared to other WSER occupations. Most skilled manual workers were taxi, bus, and truck drivers, and most non-skilled manual workers were package and food delivery persons (not reported in Results). Our study cannot shed light on the reasons for higher rates of DS in those occupations; task-related stress and unstable employment conditions may contribute. Working hours per week had effects on DS in opposite directions in the WSER and RWW models. Unlike RWWs, DS among WSERs were less likely if individuals worked 41~52 hours per week than 40 hours or less per week. Since WSER has no fixed income and is paid based on their productivity [9], DS among those working less than 40 hours per week may reflect income-related distress. Further research is needed to understand the relationships among specific jobs, employment stability, working hours, and DS.

Finally, workers lacking a rest guarantee or exhibiting SP were more likely to have fair/poor SRH and higher DS, with the effects being greater in WSERs than in RWWs. Skagen and Collin [28] reported that SP was associated with poor health status among workers, and Jeon et al. [29] reported that long working hours among Korean workers were significantly related to SP. Korean workers average 2,069 working hours annually, the second highest among Organization for Economic Co-operation and Development countries [30]. In a working environment where long working hours are prevalent, workers are forced to do their work even when they feel sick or are not guaranteed an adequate rest period between shifts, thus exposing them to health risks. According to the study results, these situations have greater effects on WSERs, who are more vulnerable in their employment relationships. The Labor Standards Act of Korea allows only 12 extended hours within a 40-hour work week. However, businesses that require 24-hour work (e.g., hospitals and transportation facilities) are permitted to guarantee an 11-hour break between shifts as a substitute for compliance with the 12-hour overtime rule. However, since WSERs are not legally designated employees, neither regulation governing employees applies to them. The results of this study suggest that the lack of an 11-hour rest period between shifts has a significant deleterious effect on the health of WSERs. Policy revision extending the 11-hour rest period to all workers may be a necessary and effective means to protect the health of WSERs and other nonstandard workers.

Some limitations of this study should be acknowledged. First, WSERs exhibit the characteristics of both employees and the self-employed. However, the subjects of this study were selected from among employees in the KWCS data; self-employed WSERs were not included because the specific question pertaining to WSER status was asked of employees only. Second, the RWW sample size was approximately 18 times larger than that of the WSER group, making it difficult to directly compare the results tested statistically. Last, this study was not able to consider the specific employment-related characteristics of WSER, such as employment stability, wage system, and absence of social security, that contribute to their vulnerable status. In the future, to uncover the pathway that explains the low health status of such workers, researchers should focus on potential associations between those specific characteristics of WSERs' employment and their health status.

Nonstandard employment is prevalent in Korea and worldwide, but research on their health has not been commensurate. This is one of the first studies to examine the health status and determinants of health of WSERs and RWWs. We reported that WSERs have poorer SRH and higher DS than RWWs and suggested several factors affecting their health status, such as a lack of rest guarantee and SP. In addition, the results of this study are reliable as they were analyzed using data representing Korean workers.

As the industrial structure in developed countries changed from manufacturing-oriented to service-oriented, various forms of nonstandard employment proliferated. Despite the increasing number of unusual and diverse forms of nonstandard employment in real life, previous research has mainly targeted part-time and temporary workers. Focusing on an important group of nonstandard employment workers, WSERs, the authors studied their health status and how different factors affected their health compared to RWWs. The results showed that WSERs, compared to RWWs, had poorer health and suggest that WSER work arrangements may confer health risks. Further investigation is needed to determine how best the demands of industry can be met while protecting worker health. Korean public health policymakers should consider measures to protect the working conditions and health of WSERs, a growing segment of the working population. This study is meaningful as it is the first report comparing the health status and health determinants of WSERs and RWWs using KWCS, a data that represents the working population in Korea.