Journal of Psychiatric Research 61 (2015) 233e234
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Letter to the Editor
Rural urban comparisons: Heterogeneity and methodological limitations
November 5, 2014 Dr. Alan Schatzberg, Editor, Journal of Psychiatric Research, Stanford University Dear Dr. Schatzberg, We are grateful to Dr. Bloomﬁeld and colleagues for raising some issues regarding the epidemiological evidence for ruralurban differences in risk for psychiatric disorders which we did not address directly in our paper. In our study, we used a large representative sample from the US which had been assessed by structured, lay administered, computer assisted face-to-face interview. Two mental health outcomes were examined, past-year major depression with functional impairment and serious mental illness (SMI). The latter outcome was deﬁned using a combination of the K6, a measure of non-speciﬁc severe psychological distress, and the WHO Disability Assessment Scale, which measures functional impairment due to mental illness. The SMI measure is not diagnosis-speciﬁc. Rather, it indicates a high predicted probability of any one of a group of serious mental illnesses assessed by standardized clinical interview in a follow-up calibration study. The prevalence of both of these outcomes, contrary to our expectations based on the existing literature, was very similar in rural and urban areas of the US, and slightly elevated in the intermediate categories of small metropolitan and semi-rural areas. This ﬁnding lead us to suggest that rural-urban differences in risk for psychiatric disorders are smaller and perhaps more heterogeneous than the current literature would suggest. Bloomﬁeld and colleagues point to studies of treated cases that ﬁnd that schizophrenia in particular is more commonly diagnosed clinically in people from urban than rural environments. Based on this literature they suggest that as yet unidentiﬁed aspects of urban environments are likely etiologic factors. Although we did not review this literature in our paper due to the reliance on treated cases, it is important to note ﬁrst that our results are compatible with an elevated prevalence of schizophrenia in urban compared with rural areas. Compared with the outcomes we examined, schizophrenia is a relatively rare disorder. A distinct rural-urban pattern of risk for schizophrenia could be obscured in the epidemiological survey data by the rural-urban patterns in more common disorders. It is important to note the limitations of relying on treatment contact for case identiﬁcation in studies of rural-urban differences in risk for schizophrenia, a disorder which is not reliably distinguished from other serious mental illnesses using the methods of
large scale population epidemiology (Kessler et al., 2005). Drawing a causal conclusion from these studies requires the assumption that the likelihood of treatment contact is essentially the same in rural and urban environments. Some authors suggest that equal probability of help-seeking across rural and urban areas is likely because schizophrenia is such a severe disorder, which is a plausible but untestable assumption. Notably, studies in the US ﬁnd disparities in mental health care between rural and urban areas (Hauenstein et al., 2007). Given the many ways that rural and urban areas differ with respect to factors known to predict clinical treatment, including availability of services, family structure, and socioeconomic status, differences in pathways to treatment may be a more parsimonious explanation of observed patterns in the prevalence of treated cases than as yet unknown etiologic factors inherent to urban environments. Bloomﬁeld and colleagues also suggest that the population survey ﬁndings may be biased due to the large number of people with mental illness who are incarcerated in the US. While the number of individuals with mental illnesses in US prisons and jails is disturbingly high, the numbers are not large enough to have a substantive impact on epidemiological estimates (Kessler, 1994). One indication that the high level of incarceration of the mentally ill in the US does not affect estimates of rural-urban differences in psychiatric disorders measured in our study is the ﬁnding that rural-urban differences do not differ between men and women (i.e. statistical interactions between urbanicity and sex were not statistically signiﬁcant). Given that many more men than women are incarcerated, we would expect to ﬁnd such a difference if incarceration had a substantive impact on the ﬁnding. Role of the funding source No funder had any role in this response letter. Contributors All four authors contributed to drafting and editing this letter. Conﬂict of interest The authors have no conﬂicts of interest to report.
Acknowledgements DOI of original article: http://dx.doi.org/10.1016/j.jpsychires.2014.11.006. http://dx.doi.org/10.1016/j.jpsychires.2014.11.009 0022-3956/© 2014 Elsevier Ltd. All rights reserved.
We have no acknowledgements for this letter.
Letter to the Editor / Journal of Psychiatric Research 61 (2015) 233e234
References Hauenstein EJ, Petterson S, Rovnyak V, Merwin E, Heise B, Wagner D. Rurality and mental health treatment. Adm Policy Ment Health Ment Health Serv Res 2007;34(3):255e67. Kessler RC. Building on the ECA: the National Comorbidity Survey and the Children's ECA. Int J Methods Psychiatr Res 1994;4:81e94. Kessler RC, Birnbaum H, Demler O, Falloon IR, Gagnon E, Guyer M, et al. The prevalence and correlates of nonaffective psychosis in the National Comorbidity Survey Replication (NCS-R). Biol Psychiatry 2005;58(8):668e76.
Joshua Breslau*, Grant Marshall RAND Corporation, USA
Harold Pincus RAND Corporation and Columbia University, Department of Psychiatry Ryan, USA Ryan Brown RAND Corporation, USA *
Corresponding author. 13 November 2014