Participation inequality in the National General Health Examination based on enterprise size

In the present study, the participation rates in WGHEs by the NHIS were higher among WPs and public officers than among RPs and dependents. Enterprise size had different effects on WGHE participation for WPs and public officers. Employee insured workers at small enterprises comprised a vulnerable group less likely to participate in WGHEs.

There are several possible reasons for the difference in the NGHE participation rate between workers (including WPs and public officers) and RPs and their dependents. Since the beginning of the WGHE, the participation rate has been higher among WPs than among RPs and their dependents [9]. First, this is because the government imposes a fine on employees for not participating in the WGHE [1, 2], while there is no enforcement for RPs and dependents. Second, the accessibility of WGHE sites is another reason for the different participation rates; while some workers are able to participate in WGHEs at their workplaces, most of RPs and their dependents should participate in NGHEs at specific healthcare institutions. Third, the ages of policyholders and their dependents might affect the participation rate. With literatures concerning on the participation rate among RPs and dependents [10, 11], an age may be determinants of NGHE participation [12]. Although workers of all age ranges should participate in the WGHE, dependents 40 years of age or older were defined as targets of the WGHE. Fourth, according to the Occupational Safety and Health Acts, all workers should participate in WGHEs, and employers should give their employees paid vacation or early leave to encourage their participation. A self-employed person without any employees is classified as a RP. Such a person will lose income by participating in a NGHE. This is also a barrier to participating in NGHEs among RPs. Fifth, participation in an opportunistic health examination is another possible reason for lower participation in WGHEs among RPs and dependents. A previous study with 10,254 participants from the Korean Longitudinal Study of Ageing revealed the difference in participation in opportunistic health examinations between employed and unemployed individuals (odds ratio for the employed: 0.86 [95% CI: 0.75–1.00; ref: unemployed]) [4]. This reflects the fact that RPs and dependents have already used the opportunistic health examination. Therefore, the participation in an organized health examination like the NGHE might be lower among RPs. Those might result in the difference in the NGHE/WGHE participation rates among policyholders in the present study. To understand why those differences in the NGHE/WGHE participation rate, a more detail consideration on barriers for the NGHE/WGHE participation should be considered.

Enterprise size significantly impacts many aspects of workers’ lives, including their health [8, 13, 14]. The participation inequality for WGHEs is shown in Fig. 2 (enterprise size 50 employees vs. ?300 employees). Historically, most small enterprises have been private companies, which might be fundamentally vulnerable [15]. The institutions administering the WGHE are unwilling to visit small enterprises due to the small number of employees who are eligible participants. Knowledge about and interest in health at small enterprises is poor [16]. Therefore, little effort has been made to improve poor workplace environments. In addition, due to the lower salary offerings, small enterprises are composed of vulnerable workers with regard to education, knowledge, physical status (unhealthy conditions), etc. At large enterprises, there is a greater guarantee of a stable labor environment (e.g., one with a labor union and welfare system) than at small enterprises [8]. With this knowledge, employees at small enterprises have been hesitant to participate in WGHEs.

As shown in Figs. 3 and 4, the WGHE participation inequalities became more prominent after the analysis was stratified by type of policyholder. Among employee insured non-office workers, those in large enterprises were previously shown to participate in the pre-employment health examination (now known as the pre-replacement health examination) than those in small enterprises (large enterprises: 89.4% vs. small enterprises: 30.4%) [17]. In addition, unhealthy workers might be forced to move to smaller enterprises, and under poor working conditions, they might lose the chance to participate in an organized health examination, even though it would be free [8, 18]. This phenomenon was also apparent in enterprises of 50–299 employees. On the other hand, WGHE participation inequalities were less likely among public officers at enterprises of 50 or 50–299 employees. The welfare system, including the health examinations of the national or local government, might support the participation of public officers in health examinations. Unstable employment conditions in Korea are less likely for public officers than for other employee insured policyholders.

Another reason for WGHE participation inequalities is the employee turnover rate at small enterprises in Korea. An issue paper evaluating the labor environment by enterprise size and type of employment revealed that the proportion of non-regular employees decreased as the enterprise size increased (the proportion of non-regular employees was 78.4% among enterprises of 50 employees vs. 14.3% among enterprises of ?300 employees) in 2013 [19]. In addition, the authors demonstrated that the proportion of short-term employees (work duration ?1 year) was higher among non-regular employees than among regular employees. The resignation rate was 0.48 for non-regular workers vs. 0.21 for regular workers in 2012 [15]. Thus, employee turnover within one year was likely at small enterprises [15]. At small enterprises, even non-office workers (who must undergo an annual WGHE) were likely to turn over in a year and lose the opportunity to participate in an annual WGHE. Therefore, efforts should be made to encourage employees at small enterprises to participate in WGHEs.

The present study had several limitations. First, policyholders were stratified into RPs and dependents, office workers, non-office workers, and public officers, but the eligible population among each category of policyholders was different in age. The enrollment criterion for dependents was being over 40 years old. Therefore, for those policyholders, the groups might have been heterogeneous. Secondly, other factors influence WGHE participation, such as the person’s socioeconomic status, position in the workplace, working duration, daily working hours, participation in shift work, marital status, but these risk factors were not included in the multiple logistic regression model. Although we searched for this information in the NHIS DB, it was not possible to access information about the work environment such as the working conditions. Nevertheless, the type of policyholder and the size of the enterprise might reflect the socioeconomic status. Third, the opportunistic health examination was not considered. Although the entire national database was assessed, it was not possible to estimate the participation in the opportunistic health examination. The opportunistic health examination should be further evaluated in future studies.

In spite of these limitations, this study also had several strengths. First, the national database powered by the NHIS was used to estimate the results. The NHIS covered about 90% of the Korean population in 2011 [20]. Therefore, our study subjects were likely to represent the population. Second, the association between enterprise size and WGHE participation was estimated after the data were stratified by the type of policyholder. As shown in Figs. 2 and 3, a negative association between the size of the enterprise and the type of policyholder was found in enterprises with 50–299 employees.