A Model of the Impact of Geographic Isolation on Mental Disability in the United States

Background and Purpose. In recent years a plethora of research results have been reported on the role of socio-cultural and other environmental conditions, particularly socioeconomic status, in the etiology and development of many types of mental illness. Geographic and social isolation has also been intermittently hypothesized to contribute to elevated rates of mental disorders, yet this body of research, with few exceptions, has not been able to invalidate competing explanations, such as spuriousness and reverse causation. One example involves its potential confounding with socioeconomic status. The current study, thus, aims to disentangle the role of geographic isolation in accounting for rates of mental disability in U.S. counties from that of low SES and related conditions.

Methods. This study employs secondary analysis, specifically, statistical modeling with national data to isolate the impact of geographic isolation on mental disability. It uses data from the U.S. Census Bureau, the CDC, and other sources, including, an index of geographic isolation developed by Doogan et al. This data is modeled with an approach to causal inference known as two-stage least squares regression with instrumental variables (2SLS-IV) which is known to effectively address problems of spuriousness and reverse causation when certain assumptions are met. It is supplemented with several other modeling methods, as well as GIS techniques.

Results. Findings reveal that the initial bivariate effects of geographic isolation on rates of mental disability are robust after controls for socioeconomic status, income inequality, social isolation, and other predictors are introduced and when tested with the 2SLS-IV procedure. Over half of the variation in county mental disability rates is accounted for by the independent effects of geographic isolation, socioeconomic status, income inequality, and other variables (F= 528.566; p<.001;R²=.544; Wald= 3289.040; p<.001). Whereas a preliminary OLS procedure indicates that the effect of geographic isolation has a ß of only .165, the 2SLS-IV procedure reveals a moderately strong effect of .370 as the independent effect of isolation on mental disability.

Conclusions and Implications. Multiple interpretations of the isolation-mental disability relationship are possible. It is, however, clear from this analysis that whatever the contributions of social isolation, low socioeconomic status, formal mental health services, or the impact of income inequality may be, that geographic isolation has a unique effect over and above these and other conditions. Perhaps one of the most salient interpretations is that proximity to others and availability of social relationships has a pervasive prophylactic effect in minimizing the risk of mental disability either in its genesis or its development, or both. The results presented, although not conclusive, supports more targeted service planning and more equitable resource investments in rural parts of the United States and other nations. These findings suggest that a range of practical interventions should be further developed for the promotion of mental health in isolated localities. These include group work and community-building interventions, such as psychiatric clubhouses; a variety of networking, outreach, and self-help methods; telehealth services; and basic services such as transportation, especially for those in rural areas.