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A population-based study of the epidemiology and influence of community violence on self-harm in California, 2005-2013

  • Author(s): Matthay, Ellicott Colson
  • Advisor(s): Ahern, Jennifer
  • et al.

Self-harm is a leading cause of morbidity and premature mortality in the United States and rates are increasing for reasons that are not well-understood. There is an urgent need to better understand the distribution and determinants of these worrisome trends and to identify effective interventions to mitigate rising rates of self-harm. A better understanding of the contribution of community-level contextual factors to self-harm incidence may help inform the design of effective prevention efforts. Community violence is an important social contextual factor that may affect self-harm, but studies to date are generally limited to small samples of adolescents and nonfatal, self-reported exposures and outcomes. Existing studies also suffer methodological limitations due to the strong correlation between community violence and other social contextual determinants of health such as income inequality.

The main objective of this dissertation was to characterize the epidemiology of self-harm in California, a large and diverse state with self-harm trends similar to those nationwide, and to systematically assess the relationship between exposure to community violence and risk of self-harm in statewide data. My first aim was to characterize trends in the epidemiology of total self-harm (completed suicide, attempted suicide and non-suicidal self-harm) and fatal self-harm (completed suicide) throughout California between 2005 and 2013, with particular focus on changes in rates and means of self-harm by demographic subgroup. My second aim was to quantify the association of exposure to overall levels of community violence with risk of self-harm and to estimate the impacts of specific changes in the distribution of community violence on self-harm corresponding to hypothetical interventions. My third aim was to quantify the association of acute increases from expected levels of community violence with risk of self-harm and to estimate the impacts of eliminating acute increases in community violence on self-harm.

To address these aims, I conducted three large, population-based studies: a descriptive study (Aim 1), a density-sampled case-control study (Aim 2), and combined case-control and case-crossover study (Aim 3). I used comprehensive statewide data on self-harm and community violence (homicide and assault) from death files from the California Department of Public Health Office of Vital Records and emergency department and inpatient hospital discharge records from the Office of Statewide Health Planning and Development (OSHPD) for the period 2005 to 2013. Cases included all deaths and hospital visits due to deliberate self-harm. Census-based denominators were used to estimate age-adjusted rates of total and fatal self-harm overall and by age, sex, race/ethnicity, county, and method of self-harm (“means”). Controls were the cases themselves (case-crossover), or California resident participants of the American Community survey matched to cases on key confounders (case-control). Community violence was measured as the rate of deaths due to homicide and injuries due to assault in the Consistent Public Use Microdata Area of residence. I estimated parameters that avoid extrapolation and capture associations of specific changes in the distribution of overall levels of community violence and acute, within-community variation in violence with risk of self-harm.

Findings suggest that total and fatal self-harm increased substantially between 2005 and 2013 in California, rising 7% and 13%, respectively. Means of self-harm changed, trending away from firearms towards suffocation and drug poisoning. Overall trends mask substantial heterogeneity across subgroups, with particularly rapid increases observed for black, multiracial, and white Californians and some rural counties. After adjustment for confounders, reducing past-year community violence to the lowest monthly levels observed within each community over the study period was 30.1 (95% CI: 29.7 to 30.6) per 100,000 lower risk of nonfatal self-harm (approximately a 13% reduction in self-harm relative to the observed risk), but no difference in the risk of fatal self-harm. Associations for a parameter corresponding to a hypothetical violence prevention intervention targeting high-violence communities indicated a 5% decrease in self-harm at the population level. In the case-crossover study, 30-day periods with higher-than-expected levels of community violence were associated with a 1.2% increased risk of fatal self-harm (95% CI: 0.3, 2.1) and a 0.7% increased risk of nonfatal self-harm (95% CI: 0.4, 0.9).

To my knowledge, this is the first study to examine trends in rates and means of fatal and nonfatal self-harm by detailed demographic subgroups in California, and the first to study the association of exposure to community violence with self-harm in a population-wide dataset. Reasons for large increases or declines in self-harm in subgroups need to be understood. Appropriate public health programming should address high-risk subgroups. Changes in means of self-harm away from those that theoretically can be restricted towards those that are not feasible to restrict highlight the need to address fundamental causes of self-harm. This study strengthens evidence on the relationship between community violence and self-harm and on the health consequences of community violence. Future research should investigate reasons for differential associations by type of community violence, type of self-harm, age, and gender, assess critical time periods of increased risk of self-harm, and determine whether violence prevention efforts have meaningful impacts on self-harm.

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