Combining individual and ecological data to determine compositional and contextual socio-economic risk factors for suicide

Abstract

The social and economic characteristics of geographic areas are associated with their suicide rates. The extent to which these ecological associations are due to the characteristics of the people living in the areas (compositional effects) or the influence of the areas themselves on risk (contextual effects) is uncertain. Denmark's Medical Register on Vital Statistics and its Integrated Database for Longitudinal Labour Market Research were used to identify suicides and 20 matched controls per case in 25–60-year-old men and women between 1982 and 1997. Individual and area (municipality) measures of income, marital and employment status were obtained. There were 9011 suicides and 180,220 controls. Individual-level associations with these risk factors were little changed when controlling for contextual effects. In contrast, ecological associations of increased suicide risk with declining area levels of employment and income and increasing proportions of people living alone were much attenuated after controlling for compositional effects. We found no consistent evidence that associations with individual-level risk factors differed depending on the areas’ characteristics (cross-level interactions). This analysis suggests the ecological associations to be attributed to characteristics of the residents rather than area influences on risk.

Introduction

Research dating back over 100 years has highlighted that individual acts of suicide could be due to forces external to individuals, reflecting the characteristics of societies (Durkheim, 1952; Morselli, 1881). Such effects have in various disciplines become known as “contextual effects” (Greenland, 2001; Joshi, 1993) and in recent years a series of ecological studies have identified factors associated with suicide rates in different geographic areas. The main factors identified are indicators of social fragmentation (anomie) and disintegration, (Ashford & Lawrence, 1976; Congdon (1996a), Congdon (2000); Saunderson & Langford, 1996; Whitley, Gunnell, Dorling, & Smith, 1999) levels of religious belief, (Neeleman, Halpern, Leon, & Lewis, 1997; Neeleman & Lewis, 1999) indicators of socio-economic position (e.g., occupation) of residents, (Congdon (1996b), Congdon (2004); Middleton et al., 2004) levels of unemployment (Congdon, 1996b; Middleton et al., 2004) and area deprivation. (Congdon (1996a), Congdon (2000); Evans, Middleton, & Gunnell, 2004)

There are two principal explanations for the associations reported in ecological studies. First, they may result from the high concentrations of at-risk individuals living in particular areas (compositional effects). For example, associations with social fragmentation may be because people at greater risk of suicide drift into these areas because of the availability of low cost housing or the anonymity these locations offer. Second, place of residence may have a real effect on suicide risk (contextual effect). Pathways for the generation of such risk may lie either in area of residence having a direct effect on the likelihood of suicidal behaviour, or in these areas being less conducive to the provision of social support for at-risk individual, both of which in turn increase suicide risk.

Area effects such as those described above may not only influence overall suicide rates in particular geographic localities, but they also may have differential effects on particular residents which depend on their personal characteristics—such as their marital status or social class. Such effects are sometimes called “cross-level effects”. (Oakes, 2004) Several sociological theories can be suggested as a firm foundation for this phenomenon, e.g. Durkheim's theory of social integration, (Durkheim, 1952) or the “Status Integration Theory” (Gibbs, 2001) formulated by Gibbs and Martin (Gibbs & Martin, 1964) which proposes that the greater the dissonance between an individual and his/her social environment, the greater their risk of suicide. A number of studies have tested the Status Integration Theory using ecological information, (Gibbs (1969), Gibbs (1982), Gibbs (2001); Gibbs & Martin, 1966; Lester (1992), Lester (1995)) but only two studies have formally examined this issue using both ecological and individual-level information in relation to suicide. (Martikainen, Maki, & Blomgren, 2004; Neeleman & Wessely, 1999) Neeleman and Wessely's London-based study of suicide and ethnicity found that as the proportion of an area's population who came from ethnic minority groups increased, so the suicide risk of people from ethnic minorities living in that area decreased whereas that for white residents increased.(Neeleman & Wessely, 1999) These findings may be interpreted as indicating that suicide risks are higher amongst people whose social and demographic characteristics differ from those of the majority of the population living in their neighbourhood—a cross-level effect. However, Martikainen's study, based on the whole of Finland, found no evidence of cross-level effects for measures of social cohesion and socio-economic position. (Martikainen et al., 2004) Furthermore, ecological associations were attenuated when controlling for individual-level variables.

Using the detailed linkage opportunities afforded by Denmark's rich series of health, social and economic registers, we investigated whether an individual's risk of suicide in relation to their marital status, employment status or income differs depending on levels of single person households, employment and income in their municipality of residence.