Social capital and violence in the United States, 1974-1993.

Social capital is a characteristic of communities. Cross-sectional studies have shown that social capital is inversely associated with homicide and violent crime. We hypothesized that variations in social capital in US states over time can predict variations in regional homicide mortality both across and within time periods. We analyzed serial cross-sectional data for measures of social capital and age-adjusted homicide rates between 1974 and 1993. We used perception of social trust and per capita membership in voluntary associations, obtained from responses to the General Social Surveys, as the principal measures of social capital. We controlled for potential confounding by mean levels of income, urbanization, and region. Measures of perceived trust were strongly inversely correlated with homicide rates in an aggregate cross-sectional analysis (r=-0.51, p<0.001) and also within each time period. Social capital was an independent predictor of rates of violence when controlling for income, region, and urbanization (p<0.001). Homicide rates also predicted levels of social capital in adjusted models (p<0.001). To investigate directionality of this relationship we developed Markov transition matrices that described the change in the states' levels of social capital and homicide across time intervals. Analysis of the transitional probabilities confirmed that a simple unidirectional association between social capital and violence was not sufficient to describe this association. There is likely an impact of violence on levels of perceived trust in communities that complements the hypothesized effect of social capital on homicide. We conclude that the relationship between social capital and violence over time is non-linear and dynamic. More complex analytic models describing the relationship between violence and ecological social determinants need to be considered.