Socioeconomic status and childhood autism: A population-based study in China
Introduction
Childhood autism, a subtype of autism spectrum disorders (ASDs) according to the International Classification of Disease, tenth revision (ICD-10) (World Health Organization, 2004) is characterized by communication and language impairments, along with repetitive stereotyped behavior and narrow interests (Duan et al., 2014, Matson et al., 2011). During past decades, the prevalence of autism rocketed from roughly 2–150 per 10,000 children in developed economies (Baron-Cohen et al., 2009, Christensen et al., 2016, Sun et al., 2014). Due to its low prevalence, conducting a nationally epidemiological investigation is time-consuming and cost-intensive and thus limited studies regarding autism were implemented in Asian nations (Khaiman et al., 2015). For example, population-based research found the prevalence of ASDs in South Korea was 2.64% and varied between institutionalized and non-institutionalized population (Kim et al., 2011). For the Chinese population, most studies on autism were conducted in Taiwan and Hong Kong, and very few studies published in English reported the prevalence of autism ranged from about 2–11 per 10,000 children in China mainland (Feng et al., 2013).
A growing number of studies have focused on the association of socioeconomic status (SES) with health outcomes (Delobel-Ayoub et al., 2015). Socioeconomic disparities in health status are often considered as avoidable and unfair, and therefore must be interrogated and addressed (Marmot, 2005). To date, however, studies on the association between SES and autism have not reached a unanimous conclusion (Rai et al., 2012). On the one hand, a large body of researches found lower SES, in the form of household income and parental education, was associated with decreased risk of childhood autism in the United States (Bhasin and Schendel, 2007, Boyle et al., 2011, Durkin et al., 2010). On the other hand, studies in European and other countries revealed negative or no relationship between SES and childhood autism. For example, an increased risk of autism was associated with lower SES in Sweden, France, and Japan (Delobel-Ayoub et al., 2015, Fujiwara, 2014, Rai et al., 2012), and no such association was found in Denmark (Larsson et al., 2005).
In China, there is very limited evidence about the relationship between SES and childhood autism. A case-control study, using hospital-based data in Zhengzhou, a central city in China, found that lower SES, measured by parental education, was related to higher risk of childhood autism (Zhang et al., 2010). In contrast with Chinese studies including single indicator of SES, studies in developed countries involved multiple socioeconomic variables to examine their independent effects on risk of autism (Bhasin and Schendel, 2007, Khaiman et al., 2015, Larsson et al., 2005, Sun et al., 2014). Therefore, in this study, we aimed to analyze the association of multiple socioeconomic circumstances with childhood autism based on a nationally population-based survey in China. Specifically, we sought to examine whether SES was associated with autism in the child, and whether there was sex difference in such association. An examination of this study would fill the gaps on this issue in China and will contribute to the world literature from the perspective of eastern social context.
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Participants
We obtained data from the Second National Sample Survey on Disability, which was conducted from April 1 to May 31, 2006 (Zheng et al., 2011). The survey aimed to estimate the distribution of individuals with different types and levels of disabilities; to examine family SES in disability; to identify the causes, timing, and medical treatment of disability; and to document the activities of disabled persons and their participation in social protection programs. The results of these surveys were
Prevalence of childhood autism by socioeconomic indicators
Table 1 shows the distributions of weighted cases and prevalence of childhood autism by socioeconomic indicators. Among all children, the prevalence of childhood autism decreased with increased household income. The highest prevalence of childhood autism was in low-education families. Housing tenure tended to present a similar pattern, with slightly lower prevalence in families with housing ownership.
Among male children, the patterning of childhood autism was similar to that among all children
Discussion
We investigated multiple socioeconomic measures regarding their association with childhood autism in a nationally population-based survey on disability in China. After the identification of mental disability according to the WHO-ICF by psychiatrists, final autistic cases were ascertained through medical diagnoses based on the ICD-10 (Li et al., 2011). To the best of our knowledge, this is the first study to report empirical results of multiple socioeconomic variables in relation to childhood
Conflicts of interest
None declared.
Acknowledgments
The authors thank the provincial and municipal federations of disabled people for their support in data collection and management. The work was supported by the Key National Project (973) of Study on the Mechanisms of Interaction between Environment and Genetics of Birth Defects in China (Grant No. 2007CB5119001), the Key State funds for social science project (Research on Disability Prevention Measurement in China, Grant No. 09&ZD072), and the State Scholarship Fund (Grant No. 201606010254).
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Ping He and Chao Guo contributed equally to the study.