Principal findings
We found that individual employment conditions were associated with the use of preventative health services such as gastric cancer screening. Self-employed and precarious workers such as temporary/daily workers and dispatched/outsourced workers exhibited lower participation rates in cancer screening than did wage workers, regular workers, and workers working in their original companies. These findings suggest that the observed disparities in equity may reflect barriers to accessing preventative healthcare services imposed by employment conditions.
The number of precarious workers is increasing worldwide, and this trend is also evident in Korea [
25]. The irregular workforce of South Korea comprises 22.3% of the entire workforce, which places the country fifth in the world in terms of the percentage of such workers. Indeed, the Korean average of 22.3% is higher than the 11.3% average for all countries in the Organization for Economic Co-operation and Development (OECD) in 2015 [
26]. Additionally, the proportion of self-employed participants in the Korean labor market is very high compared with those in other countries. For example, OECD countries tend to have fewer self-employed workers as the per capita GDP increases. However, South Korea does not fit this pattern because the income level is higher and the number of self-employed workers is also high. In 2008, one-third of the economically active population in South Korea was self-employed [
10]; in 2015, South Korea’s self-employment rate was 25.9%, ranking fifth among all OECD countries and 9.9% higher than the European Union average [
27].
Previous studies have shown that precarious employment is associated with various health problems. For example, workers with insecure jobs have higher prevalences of non-communicable diseases such as asthma and coronary heart disease [
28,
29]. Non-regular workers also exhibit high frequencies of fatigue, back pain, and musculoskeletal diseases, and they are more likely to be in poor psychological health [
30]. These groups of workers also exhibit high mortality from alcohol-related causes and smoking-related cancer, and high overall mortality rates [
8]. Self-employed workers have been considered non-standard in some studies [
31], and they experience higher levels of job-related stress and more psychosomatic health problems than do those who are not self-employed [
32]. Irregular work is associated not only with job insecurity [
33] but also with poor on-the-job training [
34] and greater exposure to hazardous work conditions [
35,
36]. All of these conditions constitute potential psychosocial and material pathways by which health can be damaged [
37]. We found disparities in the use of preventative screening by employment precariousness, suggesting that such precariousness may affect health inequities from the early stages of the ill-health spectrum.
Several mechanisms may explain the employment-associated disparities in participation in cancer screening. First, there is a loophole in the system, even though screening is provided as a social service in Korea. According to the National Health Insurance Act and the Occupation Safety Health Act of Korea, all workers who are workplace insured must periodically undergo health screening; office workers must undergo screening every 2 years, and non-office workers, every year [
38,
39]. Furthermore, the Occupational Safety Health Act states that business owners who do not facilitate worker health examinations will be fined maximum 10,000 USD (1 USD =1000 Won) [
39]. However, most irregular and self-employed workers are regionally insured rather than workplace insured, and thus are not eligible for workplace health checkups. Additionally, individuals who are workplace insured but on short contracts tend to work in the same place for less than a year, making it possible for them to be excluded from screening.
Second, and similar to the above, dispatched or outsourced irregular workers who work for small- or medium-sized companies find it difficult to participate in screening. They represent the most underprivileged workers in South Korea [
10]. Whereas workers in large companies have the opportunity to undergo regular screening, workers in small companies may suffer from the owner’s noncompliance with the duty to conduct screening programs. Thus, regular screening may be less accessible to such groups. Indeed, from 2006 to 2013, workers employed by enterprises with < 50 employees were about 50% less likely to participate in general health examinations than were those employed by enterprises with ≥300 employees [
40].
Self-employed and non-standard workers may also be unable to take the time off to participate in cancer screening. Self-employed individuals generally tend to operate in workplaces that are smaller than those of wage workers, and they also work long hours. To the extent that the income and job security of this group are similar to those of non-regular workers, self-employed workers also represent an insecure labor force. According to a 2017 report [
41], self-employed individuals with no employees comprised approximately 70% of all self-employed persons during 2000–2016 in Korea. Most of these individuals work long hours to make up for the low hourly income and do not take vacations, which can have deleterious effects on health and behavior [
42]. Non-standard workers who wish to be screened must ask for permission from the company or take unpaid time off. However, if their jobs are unstable, they would likely not take time off for screening. Indeed, non-standard workers take less sick leave, working while ill instead, because of concerns about job security and the fear of job loss [
37], despite the fact that they experience poor working conditions, are treated unfairly, and receive low wages, all of which likely increase the need for healthcare [
2,
43].
Public health implications
We found obvious inequities in the use of preventative services, according to employment conditions. Along the course of the health spectrum, it is possible that a vicious cycle may develop; individuals with precarious work receive fewer preventative services, increasing the incidence of preventable diseases, rendering the economic situation even more difficult. It is necessary for institutions to commit to breaking this cycle. We found that employment conditions per se were independently associated with the use of preventative services, even after controlling for sociodemographic factors such as income and educational level. As employment conditions are associated with wages, occupational safety, and job security, such conditions interact with sociodemographic factors to influence individual health status and the use of health services. However, our findings suggest that relatively simple interventions would allow equitable access to health services, unlike the interventions required to influence other sociodemographic factors.
From the perspective of improving the national cancer screening rate, it is clear that the use of cancer screening services is affected by employment characteristics and insecurity. As mentioned above, biennial gastric cancer screening for those aged ≥40 years is free for Medicaid enrollees and NHI beneficiaries in the lower half of the income strata, and is inexpensive (only 10% of the real cost) for NHI beneficiaries in the upper half of the income strata. This suggests that barriers other than financial barriers exist. Korea has made various efforts to improve cancer screening rates, and the gastric cancer screening rate did increase from 39.2% in 2004 to 73.6% in 2013 [
19]. It seems that any improvements in cancer screening rates obtainable via individual encouragement have now been attained. In fact, we found that further adjustment of health-related behavior (which is correlated with individual health commitment) did not significantly change the outcome (Model 3 vs. Model 2 in Table
2). Given that it is necessary to further improve cancer screening rates, a social approach must be added to individual encouragement.
Limitations
Our study had several possible limitations. First, as the work was cross-sectional in design, it was impossible to determine causal associations between employment conditions and the use of preventative services. Second, both employment status and cancer screening data were self-reported and therefore subject to a degree of inaccuracy. Third, we studied cancer screening only. Further studies are needed to determine whether inequities caused by employment are apparent in the use of other preventative health services such as general health examinations or influenza vaccination. Also, although other cancer screening programs were not included in our study because they did not target the entire population or targeted only older people (reducing the relevance to employment status), it is necessary in the future to investigate whether similar patterns appear when other cancer screening systems are examined. Fourth, although we chose gastric cancer screening to study employees of a wide age range, all ages were not included in the study because eligible age of undergoing gastric cancer screening is over 40 years. In this regard, further investigation of preventive services used by all age groups is needed.
Despite these limitations, our findings are meaningful because the numbers of irregular and the self-employed workers are increasing in Korea, exacerbating health-related problems. Previously, Kim et al. [
44] reported a study on cancer screening participation according to job status using 2013 KNHANES data. The study showed that part-time workers were less likely to participate in cancer screening than full-time workers. However, due to a limitation in available survey variables, the study included only wage workers. In our study, we used the 2008–2009 KNHANES data which includes more abundant work-related variables. As a result, we were able to analyze not only wage workers, but also self-employed workers, unpaid family members, and other workers. In addition, we were able to carry out in-depth analysis for wage workers and consider whether they were regular workers (aspects of employment contract term and job security) or dispatched workers (aspects of salary source and business command). To the best of our knowledge, this is the first study to explore disparities in the use of preventative services by various employment characteristics (occupation type, industry, work schedule, and precariousness) and various types of precariousness (work hours, employment contract term, and salary source business command) using nationally representative data.