Depression and associated factors in internal migrant workers in China

Abstract

Background

Internal migrant workers are a large population in China. Current health related studies among this population mainly focused on infectious disease, maternal health and occupational diseases and injuries. However, very limited studies were paid attention to mental health of migrant workers though it is an important public health issue.

Aims

The current study aims to understand prevalence of depression symptoms and factors associated with depression among Chinese migrant workers using novel methods to develop a comprehensive sample.

Methods

Respondent-driven sampling (RDS) was employed to recruit the target population, who are required 1) not to hold a hukou indicative of living in central areas or near suburbs of Chengdu city; 2) to be 16 years or older; 3) not to be a student. The Center for Epidemiologic Depression Scale (CES-D) was used to measure depression symptoms of migrant workers. And then Structural Equation Model (SEM) was applied to explore factors associated with depression among Chinese migrant workers.

Results

Among 1180 migrant workers, 23.7% of them had clinically relevant depression symptoms (CES-D score >= 16), and 12.8% were consistent with a clinical diagnosis of depression (CES-D score >= 21). Self-rated economic status, city adaptation status, and self-rated health had negative effects on depression. Social economic status (SES) affected depression, and was mediated by self-rated economic status and self-rated health. City adaptation status was affected by length of residence in the city, satisfaction with one's job, and the social support that one could obtain while living in the city.

Conclusions

The findings indicated a higher prevalence of depression symptoms among migrant workers comparing to general population reported by previous studies, identified possible factors associated with depression symptoms, and also explored relationships between these factors. Our study provides a model to understand mental health of Chinese internal migrant workers and to generate important research questions for the future.

Introduction

China is experiencing the largest in-country migration in history. Data in The 2010 Report on the Development of China's Migrant Population (National Population and Family Planning Commission of P.R. China, 2010) showed that China's migrant population had reached 211 million in 2009. Migrant workers are defined as people who are 16 years and older, and who leave their hukou (registered residence in China) to work in another place.

Internal migration in China occurs without a change in hukou status. For decades, the hukou system had functioned like an “internal passport system,” where a person's hukou defined access to employment, housing, social welfare, and educational opportunities (Chan, 1996). When strictly enforced in times past, one's hukou defined where an individual could live and work (Roberts, 1997); while the use of a person's hukou to control internal mobility has relaxed greatly during the recent decades of economic transformation, with many rural migrants moving to metropolitan manufacturing and construction centers to supply the needed workforce for China's robust economic expansion, it continues to influence access to employment, social welfare, education, and health services.

Researchers in the United States and the United Kingdom have described elevated levels of morbidity due to mental disorders among immigrants, particularly depression and anxiety (Aroian and Norris, 2003, Burvill et al., 1983, Cuellar et al., 2004, Hovey and Magana, 2000, Kimura et al., 1975, Murray and Williams, 1986). Investigations of factors possibly contributing to their susceptibility have implicated a combination of rapid personal changes together with disorganization of migrants' psychosocial contexts, and family and social systems (Heilemann et al., 2004, Mann, 2004, Shen and Takeuchi, 2001). Thus far, current research on migrants' health in China has focused principally on infectious diseases, maternal health, and occupational disease and injuries (Hu, 2008). The general mental health of migrant workers in China, not to mention the depression, has received relatively less attention. Depression-related disability, in particular, has a powerful impact on workforce productivity that in turn threatens economic development and the harmony and stability of society.

The few studies now available suggest that depression may be a serious problem among China's internal migrants. Chen et al. (2006) employed the Self-Rating Depression Scale (SDS) to investigate depressive symptoms; the mean score among migrants was significantly higher than the norm for the general population, and the prevalence of depressive symptoms was 34.2%. Lin et al. (2006) investigated 866 female migrant workers in Beijing using the Center for Epidemiological Studies — Depressed (CES-D) scale, finding that 23% female migrants had clinically relevant depressive symptoms. Taken together, the relatively few available studies suggest that the mental health status of internal migrant workers requires further study.

The study that we report was conducted in Chengdu, the capital of Southwest China's Sichuan Province, with a population of 12.87 million in 2009. While Sichuan is one of the provinces to export migrant workers, Chengdu itself receives a large number of migrant workers from other cities in the province and from poor rural areas. According to the 2009 data from Chengdu Bureau of Statistics, there were 1.47 million migrants in Chengdu, 11.4% of the total population. Despite this large scale of migration, their mental health needs receive little attention. Wang's study on anxiety of migrants in Chengdu found a higher prevalence of anxiety symptoms compared with general population (Wang et al., 2007). This may indicate a high level of distress among this population, which in turn could influence quality of life and even compromise workforce productivity.

In this study, we survey the prevalence of depression symptoms using CES-D among Chinese migrant workers, and then explore factors associated with depression symptoms and interactions between them. Results from previous studies on potential factors associated with depression symptoms were used to form the theoretical framework for Structural Equation Model (SEM).

Several studies in general population found that subjects with lower SES were more likely to be depressed than those with higher SES (Huurre et al., 2007, Molarius et al., 2009). Also, research in immigrants indicated SES was inversely related to mental health status (Gresenz et al., 2001). The possible reasons might be people with lower SES will encounter a great number of stressful life events, and they have fewer resources to address difficulties (Kim et al., 2005). Chinese internal migration is economic-driven migration. Rural people leave their lands to earn money in the cities, and people from western areas migrate to east coast areas in order to improve their income. However, many times, they are facing discriminatory treatment in terms of working hours, payment, living and working environment, education and social welfare (Dong and Bowles, 2002), experiencing low SES. In the study, we examine explicitly whether SES will negatively relate to depressive symptoms. Several authors (Hu et al., 2005, Kopp et al., 2004, Operario et al., 2004, Singh-Manoux et al., 2003) argue that “subjective SES,” related to one's sense of economic wellbeing, has a stronger relationship to health status than objective measures of SES. In our study, we investigated the subjective SES of respondents as well as other measures, and expected that it would show a negative relation with depressive symptoms.

Many previous studies have indicated an association between the presence of depressive symptoms and medical conditions such as diabetes, stroke, myocardial infarction, congestive heart failure, and cancer (Carney and Freedland, 2003, Frasure-Smith et al., 1993, Katon, 2003, Koenig, 1998, Pohjasvaara et al., 1998). Thus we proposed that poor health contributes to depressive symptoms. Migrant workers are usually regarded as young and healthy, and few of them suffer from chronic diseases. Nonetheless, many of them will take dirty and dangerous work that local residents avoid, and this in turn may affect their health status. Moreover, not all migrant workers have intact health status; we encountered disabled workers who worked in massage shops or as parking attendants. In our study we posited that better health would be associated with fewer depressive symptoms.

The effect of social support on depression has been well documented (Badger and Collins-Joyce, 2000, Chou, 2009, Fagg et al., 2008, Hovey, 2000, Norah, 2007). Buffer effect theory suggests that social supports act as a buffer to environmental stresses, which may decrease one's susceptibility to mental disorders (Caplan and Caplan, 2000). In many cases, moving from one place to another to live and work means attenuation or loss of an individual's old social network and support. Thus, migration for work, which may not entail the development of new permanent networks, may place individuals at greater risk for mental distress or disorders. Chinese workers tend to migrate with their relatives, friends and people from the same location (Lao Xiang), which could mitigate the effects from losing social network and support. Nonetheless, we would anticipate that changes of social network and social support will adversely affect their mental health. We hypothesized that a lesser degree social support would be associated with higher reported symptoms of mental distress.

Acculturation is reported by the previous studies to be another potentially important, though controversial factor for depression in immigrants (Kim et al., 2005, Miranda and Umhoefer, 1998, Nguyen and Peterson, 1993, Rivera, 2007, Shen and Takeuchi, 2001). Cultural identity, language proficiency and cultural competence were used in the previous study to measure acculturation of migrants (Park and Bernstein, 2008, Rivera, 2007). Despite China's regional linguistic and cultural diversity, migrant workers do not face many of the challenges experienced by international immigrants. Moreover, 90% of Chengdu's migrants are drawn from other cities in Sichuan Province and from Chongqing, where people have similar dialects and cultures (Tang, 2006). Thus, measuring city adaptation is more appropriate in our sample. While most migrant workers in Chengdu do not face language and cultural, they like others confront the substantial rural-to-urban transition that is common in major Chinese industrial zones that draw from distant regions. In our study, we examined this city adaptation, and expected that migrants who reported more positive adaption also would evidence better mental health.

Several previous studies have reported that duration of migrant status was associated with depression (Kim et al., 2005, Lai, 2004). They found that the longer migrants stay in the new environment, the better they could adapt themselves to the environment. Additional contributing factors, irrespective of migrant status, may include female gender (Kessler et al., 1994), genetic risk factors (i.e. a positive family history of depression) (Lieb et al., 2002), psychiatric disorders of the individual (Aalto-Setala et al., 2002), marital status (Prigerson et al., 1994), job satisfaction (Lee et al., 2009), and negative life events (Hammen, 1992, Prigerson et al., 1994). Since psychiatric illness is a sensitive topic in China, we did not ask respondents' history of psychiatric illness. Instead, we did ask if there was any family member with psychiatric illness. However, there are only four respondents reported having family members with psychiatric illness so that we did not include it in the analysis.

Factors such as the ones that we have discussed may variably contribute to both the development and severity of depression symptoms. They do not function independently. For example, objective SES likely will influence subjective SES, city adaptation, and self-rated health. And level of social support, duration of migration, and job satisfaction may influence reported city adaptation.