ASS CONFLICT AND DISplacement continue to affect large numbers of people worldwide. 1 In 2007, the United Nations High Commissioner for Refugees documented 16 million refugees, 26 million internally displaced persons, and 12 million stateless persons. 2 Yet controversy about the mental health needs of conflictexposed populations persists, 3 a problem that is magnified by the wide variability in rates of the most commonly studied psychiatric conditions among affected populations, namely, posttraumatic stress disorder (PTSD) and depression. Prevalence rates for PTSD have ranged from 0% in a conflict-affected region of Iran 4 to 99% in Sierra Leone 5 and between 3% and 86% for depression across surveys. 6,7 Identifying the potential methodological and substantive factors that are associated with this variation is vital to determining with any accuracy rates of mental health problems of conflict-affected populations.Methodological factors, particularly the approach used for sampling and diagnosis, appear to exert a large influence on the prevalence rates yielded by surveys. 8 An outstanding question, how-Author Affiliations are listed at the end of this article.

Despite a substantial degree of inter-survey heterogeneity in the meta-analysis, the findings confirm that common mental disorders are highly prevalent globally, affecting people across all regions of the world. This research provides an important resource for modelling population needs based on global regional estimates of mental disorder. The reasons for regional variation in mental disorder require further investigation.

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