Education and income: which is more important for mental health? (Research Report).

Study objective: To assess which indicators of socioeconomic status are associated with an increased prevalence of common mental disorders.

Design: Cross sectional household survey.

Setting: Santiago, Chile.

Participants: Random sample of adults aged 16-65 residing in private households.

Main results: Less education (odds ratio 2.44, 95% confidence intervals 1 .50 to 3.97), a recent income decrease (odds ratio 2.14, 1.70 to 2.70), and poor housing (odds ratio 1.53, 1.05 to 2.23), were the only socioeconomic status variables that remained significantly associated with an increased prevalence of common mental disorders after adjustments. The prevalence of common mental disorders was also higher among people with manual unskilled occupations, overcrowded housing, and lower per capita income but these associations disappeared after adjustment for other explanatory and confounding variables.

Conclusions: There is a strong, inverse, and independent association between education and common mental disorders. However, income was not associated with the prevalence of common mental disorders, after adjusting for other socioeconomic variables. Similar results have been found in other Latin American studies but British studies tend to find the opposite, that income but not education is associated with common mental disorders. Understanding the impact of socioeconomic factors on mental health requires research in poor as well as rich countries.

**********

According to the World Health Organisation much of the global health burden is attributable to the nonpsychotic and common mental disorders, such as depression and anxiety. (1) Although some psychotic conditions might be more severe and burdensome on an individual basis, the volume and duration of the more common mental conditions yield a much larger aggregate burden.

Socioeconomic status is a complex concept that has been borrowed by medical researchers, often without due regard to its sociological inheritance. In epidemiology the concept is assessed indirectly using a variety of different measures with different implications for social and economic policy. Income, material possessions (or standard of living), occupational status, and education are the domains most commonly studied. Nevertheless, these measures are not equivalent and might have different meanings and represent different concepts of social position in different cultures. For instance, income changes throughout life while education remains comparatively "frozen" after early adulthood and educational attainments can have different meaning in different places. The association between relative or absolute income and health is among the most commonly reported in the scientific literature. However, several recent studies have found that this association is weakened or disappear when controlling for other socioec onomic variables, especially education. (2-4) Understanding the relation between socioeconomic status and health depends upon distinguishing these various measures and examining for independent associations with health.

A large body of scientific literature, mainly from western countries, shows that social disadvantage, especially lack of material possessions, lower income, and financial strain, are associated with common mental disorders (CMD). (5-9) However, much less is known of the socioeconomic determinants of CMD in non-western countries. Nevertheless most of the world's population live outside the western countries and it is these developing countries that experience the largest degree of socioeconomic inequality. Psychiatric household surveys from these countries rarely get published in peer reviewed journals. (10) There have been a few published from Latin America over the past 20 years. (11-13) but because of some methodological problems, especially the lack of adjustment for potential explanatory or confounding variables no firm conclusions can be reached. Thus it is still unclear which socioeconomic factors, if any, are independently associated with an increased prevalence of CMD in Latin America and elsewhere in the developing world.

There seems to be an important gap in our knowledge about the most accurate indicators of social position and the most health sensitive socioeconomic factors across cultures. To understand better the relation between socioeconomic status and mental health, we need to carry out research in rich as well as poor countries. We carried out a large cross sectional survey of the private households of Santiago, the capital of Chile to examine which indicators of socioeconomic status are most strongly associated with the prevalence of CMD.

METHODS

Participants and sampling

This paper describes data from the Santiago Mental Disorders Survey undertaken between 1996 and 1998 in Santiago, Chile. (14) The sampling involved a three stage clustered design. Households within 200 sectors from all the 35 boroughs of Santiago, capital of Chile, were randomly chosen with a probability proportional to the population size. A larger sampling fraction was needed in the most affluent boroughs to permit testing for socioeconomic differences between groups. One person per household was chosen at random. (15) The sampling framework was the total adult population living in private households of Santiago, representing 3 217 177 people. Further details of the sampling design can be requested from the authors.

Variables

Main outcome variable

CMD were assessed using the Revised …