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OBJECTIVE: To test whether rates of bipolar disorder (BD) have changed over time or vary across geographic regions after adjusting for design features meta-analyzing epidemiologic studies reporting BD prevalence in adults worldwide. DATA SOURCES: Searches in PubMed and PsycINFO using the terms (epidemiology OR community OR prevalence) AND (mania OR "bipolar disorder" OR cyclothymi*) AND adult and backward searches from published reviews were conducted. STUDY SELECTION: Eighty-five epidemiologic studies published in English from 1980 onward that reported prevalence rates for BD or mania for subjects ≥ 18 years old were included. DATA EXTRACTION: We coded BD prevalence, method of data collection, diagnostic criteria, year of study, country, and quality of study design and data reporting. Meta-regression tested whether sample characteristics influenced prevalence rates using the metafor package in R. RESULTS: Eighty-five effect sizes, from 44 countries, from studies spanning the years 1980-2012, included 67,373 people with BD. Lifetime prevalence for BD spectrum was 1.02% (95% CI, 0.81%-1.29%). Prevalence was moderated by the inclusion of BD not otherwise specified (P = .009) and by geographic region; rates from Africa and Asia were less than half of those from North and South America. Rates did not change significantly over 3 decades after controlling for design features. CONCLUSIONS: The overall prevalence rate is consistent with historical estimates, but rates vary significantly across studies. Differences in methodology contribute to the perception that rates of BD have increased over time. Rates varied markedly by geographic region, even after controlling for all other predictors. Research using consistent definitions and methods may expose specific factors that confer risk for BD.
Moreira et al. (Mon,) studied this question.