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Brazilian Journal of Psychiatry

Print version ISSN 1516-4446On-line version ISSN 1809-452X

Rev. Bras. Psiquiatr. vol.37 no.2 São Paulo Apr./June 2015  Epub May 01, 2015

http://dx.doi.org/10.1590/1516-4446-2012-1693 

Review Articles

Bipolar disorder prevalence: a systematic review and meta-analysis of the literature

Adauto S. Clemente1 

Breno S. Diniz2  3 

Rodrigo Nicolato2 

Flavio P. Kapczinski4  5 

Jair C. Soares5 

Josélia O. Firmo1 

Érico Castro-Costa1 

1Centro de Pesquisas René Rachou, Fundação Oswaldo Cruz, Belo Horizonte, MG, Brazil

2Department of Mental Health, School of Medicine, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil

3National Science and Technology Institute for Molecular Medicine (INCT-MM), UFMG, Belo Horizonte, MG, Brazil

4Molecular Psychiatry Laboratory, National Science and Technology Institute for Translational Medicine (INCT-TM), Hospital de Clínicas de Porto Alegre (HCPA), Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil

5Center of Excellence on Mood Disorders, Department of Psychiatry and Behavioral Sciences, University of Texas Health Science Center, Houston, TX, USA

ABSTRACT

Objective:

Bipolar disorder (BD) is common in clinical psychiatric practice, and several studies have estimated its prevalence to range from 0.5 to 5% in community-based samples. However, no systematic review and meta-analysis of the prevalence of BD type 1 and type 2 has been published in the literature. We carried out a systematic review and meta-analysis of the lifetime and 1-year prevalence of BD type 1 and type 2 and assessed whether the prevalence of BD changed according to the diagnostic criteria adopted (DSM-III, DSM-III-R vs. DSM-IV).

Methods:

We searched MEDLINE, Scopus, Web of Science, PsycINFO, and the reference lists of identified studies. The analyses included 25 population- or community-based studies and 276,221 participants.

Results:

The pooled lifetime prevalence of BD type 1 was 1.06% (95% confidence interval [95%CI] 0.81-1.31) and that of BD type 2 was 1.57% (95%CI 1.15-1.99). The pooled 1-year prevalence was 0.71% (95%CI 0.56-0.86) for BD type 1 and 0.50% (95%CI 0.35-0.64) for BD type 2. Subgroup analysis showed a significantly higher lifetime prevalence of BD type 1 according to the DSM-IV criteria compared to the DSM-III and DSM-IIIR criteria (p < 0.001).

Conclusion:

This meta-analysis confirms that estimates of BD type 1 and type 2 prevalence are low in the general population. The increase in prevalence from DSM-III and DSM-III-R to DSM-IV may reflect different factors, such as minor changes in diagnostic operationalization, use of different assessment instruments, or even a genuine increase in the prevalence of BD.

Key words: Bipolar disorder; prevalence; meta-analysis; DSM-III; DSM-III-R; DSM-IV

Introduction

Bipolar disorder (BD) is a common disorder associated with functional and cognitive impairment,1,2 negative health outcomes,3,4 and increased risk of suicide.5 In the last decades, clinical observations have challenged the traditional concepts of BD, suggesting that its manifestations occur over a broad spectrum of severity, i.e., the bipolar spectrum.6,7 The identification of subjects in the bipolar spectrum that do not meet the criteria for BD type 1 or BD type 2 has had a significant impact on BD epidemiology, with a substantial increase in its prevalence.8,9

Since the introduction of official manuals for diagnosis and classification in psychiatry, prevalence estimates of BD have changed significantly over time. In a systematic review of community-based studies published between 1950 and 1980, the authors found that the prevalence of affective psychosis ranged from 1.2 to 69.0% in 12 of the U.S. studies.10 Some methodological issues may help explain such variance, such as the lack of well-established diagnostic criteria for affective psychosis and the fact that most of the studies estimated its prevalence from records of psychiatric inpatient services or unsystematic community studies.

The first epidemiological study based on DSM-III criteria11 estimated the lifetime prevalence of BD as 1% in the general population.12 In the 1990s, the DSM-IV further divided this diagnostic category into three major groups: BD type 1, BD type 2, or BD mixed episode.13 Further community- and population-based epidemiological studies using ICD and DSM diagnostic criteria estimated the lifetime prevalence of BD as 1.0-2.0%.14

However, concerns that the prevalence of BD is underestimated in the general population have emerged in the literature.15Sequential monitoring of the Zurich cohort8found that several episodes of hypomania cannot be readily recognized by traditional criteria and, thus, the authors proposed more flexible criteria for episode duration and number of symptoms required for diagnosis. Reduction of the duration criteria of hypomania from 4 to 2 days increased the number of BD type 2 cases tenfold, thus increasing its prevalence in this cohort from 0.5 to 5.0%. The inclusion of other subtypes, such as subsyndromal BD and pure hypomania, increased the prevalence of the bipolar spectrum to 10.9% of the population. Nonetheless, there are no consensus criteria for bipolar spectrum, and estimates from population-based studies are highly variable, making it difficult to compare the results of different studies.

Although systematic reviews on the prevalence of BD have been previously published,14,16,17 we have not identified studies that have statistically treated their findings through meta-analysis. This is important, since the meta-analytic approach can yield more reliable prevalence estimates, in particular for conditions with low prevalence, such as BD. In addition, the diagnostic criteria for BD have changed over time and no study has addressed whether such changes affected BD prevalence. Therefore, we sought to carry out a systematic review and meta-analysis of the prevalence of BD from population-based studies. We evaluated the lifetime and 1-year prevalence of BD type 1 and BD type 2. Finally, we compared whether the prevalence of BD changed according to the diagnostic criteria adopted (DSM-III, DSM-III-R vs. DSM-IV).

Methods

Search strategies

We carried out this systematic review and meta-analysis according to the MOOSE (Meta-analysis Of Observational Studies in Epidemiology) guidelines.18

We searched the MEDLINE (through PubMed), SCOPUS, Web of Science, and PsycINFO databases in October 2013, using the following search terms: (“bipolar disorder OR bipolar spectrum”) AND (“prevalence OR epidemiology OR community-based OR population-based”). We used the search filters [Title/Abstract] PDAT in PubMed; [Title/Abs/Key] in Scopus; [Title] in Web of Science; and [Any Field] on PsycINFO. We limited the search to articles published between January 1, 1980 and September 30, 2013. Other relevant articles were identified by means of a hand search of the references of selected articles, from previously published reviews on the subject, and from transnational surveys for mental disorders, such as the ICPE,19 and the WMH Survey initiative.20

Inclusion and exclusion criteria

The criteria for inclusion of studies in the meta-analysis were: 1) original articles reporting the prevalence of BD in adults; 2) studies that used operationalized diagnostic criteria and standardized instruments or clinical diagnosis based on the DSM-III, DSM-IIIR, or DSM-IV; 3) community or population-based studies; and 4) articles published in English. We excluded articles from studies that used indirect methods to estimate prevalence (such as records of medical attendance), that did not distinguish the prevalence of BD from that of other affective disorders, or that evaluated clinical samples or specific subpopulations, such as immigrants, ethnic groups, or institutionalized groups.

Data extraction and statistical analysis

For each study, we extracted the following information: authors, year of publication, country, sample size, diagnostic criteria, assessment instrument, and sample recruitment design. We extracted the prevalence and the respective standard error (SE) or 95% confidence interval (95%CI) for BD type 1 and/or type 2 when available. Some studies that did not report the SE or the 95%CI were included if the 95%CI could be calculated using Newcombe’s methods.21 Study selection and data extraction from the relevant articles were performed independently by two researchers (ASC and ECC). If conflicts remained as to study selection and data extraction, a third researcher (BSD) decided about the inclusion or exclusion of the study or data in the meta-analysis.

We used the generic inverse variance method with a random-effects model for all analyses. Random-effects models are more appropriate than fixed-effect models to deal with studies characterized by heterogeneous methodological approaches, such as those included in this meta-analysis. We assessed heterogeneity in the meta-analysis by means of the Q-test and I2 index. If the p-value was below 0.05 in the Q-test and/or the I2 index was higher than 50%, the pooled analysis was considered to be significantly heterogeneous.

We performed sensitivity analyses by excluding one study at a time and recalculating the risk effect to evaluate whether the summary risk effect was significantly influenced by any individual study. Publication bias was ascertained by visual inspection of a funnel plot. All analyses were carried out with the RevMan 5.1 statistical software (The Nordic Cochrane Centre, Copenhagen, Denmark, http://ims.cochrane.org/revman/download) in Windows 7.

Results

Figure 1 Flow diagram of selection strategy. 

Figure 1 shows a flow chart of the study search and selection process for inclusion in the meta-analysis.

We included 25 studies from 15 countries, for a total of 276,221 participants, in the meta-analysis. Tables 1 to 4 show the main characteristics of individual studies.

Table 1 Summary of studies of bipolar disorder type 1 included in the meta-analysis (lifetime prevalence) 

Study Country Coverage Sample size (n) Age range (years) Diagnostic criteria Tool Prevalence (%) SE
Angst22 United States National 9,282 18-99 DSM-IV CIDI 3.0 0.70 0.10
Canino23 Puerto Rico National 1,551 17-64 DSM-III DIS 0.50 0.20
Chong24 Singapore National 6,616 18-99 DSM-IV CIDI 3.0 1.20 0.20
Fogarty25 Canada Community 3,258 18-99 DSM-III DIS 0.60 0.10
Hoertel26 United States National 43,093 18-99 DSM-IV AUDADIS-IV 2.19 0.11
Hwu27 Taiwan Community 11,004 18-99 DSM-III DIS-II 0.16 0.06
Jonas28 United States National 7,667 17-39 DSM-III DIS 1.20 0.30
Judd29 United States National 18,252 18-99 DSM-III DIS 0.80 0.09
Keqing30 China Community 20,716 18-99 DSM-IV-TR GHQ-12/SCID-I 1.97 0.61
Kessler31 United States National 8,098 15-54 DSM-III-R UM-CIDI 1.60 0.30
Kessler32 United States National 8,098 15-54 DSM-III-R UM-CIDI 0.45 0.14
Kessler33 United States National 5,223 18-64 DSM-IV-TR WMH-CIDI 1.10 0.20
Lee34 South Korea Community (Seoul) 5,100 18-64 DSM-III DIS-III 0.40 -
Levav35 Israel National 2,741 24-33 RDC SADS-L 0.70 0.10
Moreno36 Brazil Community 1,464 18-99 DSM-III-R CIDI 0.50 0.20
Negash37 Ethiopia Regional 68,378 15-49 DSM-IV CIDI/SCAN 1.20 0.20
Regier38 United States Regional 20,861 18-99 DSM-III DIS 0.60 0.10
Szádóczky39 Hungary Regional 2,953 18-64 DSM-III-R DIS 2.19 0.11
Vega40 United States Community 3,012 18-59 DSM-III-R CIDI 0.16 0.06
Vicente41 Chile Regional 2,987 15-99 DSM-III-R CIDI 1.0/1.1 1.20 0.30

AUDADIS-IV = Alcohol Use Disorder and Associated Disabilities Interview Schedule-IV; CIDI = Composite International Diagnostic Interview; DIS = Diagnostic Interview Schedule; GHQ-12 = General Health Questionnaire; RDC = Research Domain Criteria; SADS-L = Schedule for Affective Disorders and Schizophrenia-Lifetime; SCAN = Schedule for Clinical Assessment in Neuropsychiatry; SCID = Structured Clinical Interview for DSM Disorders; SE = standard error; UM-CIDI = University of Michigan - Composite International Diagnostic Interview; WMH = World Mental Health.

Table 2 Summary of studies of bipolar disorder type 1 included in the meta-analysis (12-month prevalence) 

Study Country Coverage Sample size (n) Age range(years) Diagnostic criteria Tool Prevalence (%) SE
Angst22 United States National 9,282 18-99 DSM-IV CIDI 3.0 0.30 0.10
Chong24 Singapore National 6,616 18-99 DSM-IV CIDI 3.0 1.20 0.20
Faravelli42 Italy Community 1,000 15-99 DSM-III Psychiatric examination 1.30 0.40
Hoertel26 United States National 43,093 18-99 DSM-IV AUDADIS-IV 0.87 0.06
Keqing30 China Community 20,716 18-99 DSM-IV-TR GHQ-12/SCID-I 1.25 0.48
Kessler31 United States National 8,098 15-54 DSM-III-R UM-CIDI 1.30 0.20
Kessler32 United States National 8,098 15-54 DSM-III-R UM-CIDI 0.37 0.14
Kessler33 United States National 5,223 18-64 DSM-IV-TR WMH-CIDI 0.70 0.10
Lee34 China Community 3,016 18-65 DSM-IV BDS 1.40 0.23
Mitchell43 Australia National 8,841 16-85 DSM-IV WMH-CIDI 0.50 0.10
Parikh44 Canada (rural areas) Regional 8,116 15-64 DSM-III-R UM-CIDI 0.40 0.15
Parikh44 Canada (urban areas) Regional 8,116 15-64 DSM-III-R UM-CIDI 0.60 0.05
Regier38 United States Regional 20,861 18-99 DSM-III DIS 0.50 0.10
Vicente41 Chile Regional 2,987 15-99 DSM-III-R CIDI 1.0/1.1 1.40 0.30
Wells45 New Zealand National 12,992 16-99 DSM-IV CIDI 3.0 0.60 0.07

AUDADIS-IV = Alcohol Use Disorder and Associated Disabilities Interview Schedule-IV; BDS = Behavior Dimension Scale; CIDI = Composite International Diagnostic Interview; DIS = Diagnostic Interview Schedule; GHQ-12 = General Health Questionnaire; SADS-L = Schedule for Affective Disorders and Schizophrenia-Lifetime; SCID = Structured Clinical Interview for DSM Disorders; SE = standard error; UM-CIDI = University of Michigan - Composite International Diagnostic Interview; WMH = World Mental Health.

Table 3 Summary of studies of bipolar disorder type 2 included in the meta-analysis (lifetime prevalence) 

Study Country Coverage Sample size (n) Age range(years) Diagnostic criteria Tool Prevalence (%) SE
Angst22 United States National 9,282 18-99 DSM-IV CIDI 3.0 1.60 0.20
Hoertel26 United States National 43,093 18-99 DSM-IV AUDADIS-IV 1.12 0.07
Keqing30 China Community 20,716 18-99 DSM-IV-TR GHQ-12/SCID-I 1.30 0.49
Kessler33 United States National 5,223 18-64 DSM-IV-TR WMH-CIDI 1.40 0.10
Lee34 China Community 3,016 18-65 DSM-IV BDS 2.20 0.28
Levav35 Israel National 2,741 24-33 RDC SADS-L 0.57 0.31
Moreno36 Brazil Community 1,464 18-99 DSM-III-R CIDI 0.70 0.20
Szádóczky39 Hungary Regional 2,953 18-64 DSM-III-R DIS 2.00 0.50

AUDADIS-IV = Alcohol Use Disorder and Associated Disabilities Interview Schedule-IV; BDS = Behavior Dimension Scale; CIDI = Composite International Diagnostic Interview; DIS = Diagnostic Interview Schedule; GHQ-12 = General Health Questionnaire; RDC = Research Domain Criteria; SCID = Structured Clinical Interview for DSM Disorders; SE = standard error; WMH = World Mental Health.

Table 4 Summary of studies of bipolar disorder type 2 included in the meta-analysis (12-month prevalence) 

Study Country Coverage Sample size (n) Age range (years) Diagnostic criteria Tool Prevalence (%) SE
Angst22 United States National 9,282 18-99 DSM-IV CIDI 3.0 0.80 0.10
Faravelli42 Italy Community 1,000 15-99 DSM-III Psychiatric examination 0.20 0.05
Hoertel26 United States National 43,093 18-99 DSM-IV AUDADIS-IV 0.32 0.04
Keqing30 China Community 20,716 18-99 DSM-IV-TR GHQ-12/SCID-I 0.48 0.30
Kessler33 United States National 5,223 18-64 DSM-IV-TR WMH-CIDI 1.00 0.10
Lee34 China Community 3,016 18-65 DSM-IV BDS (telephone interview) 0.50 0.12
Mitchell43 Australia National 8,841 16-85 DSM-IV WMH-CIDI 0.40 0.10
Wells45 New Zealand National 12,992 16-99 DSM-IV CIDI 3.0 0.40 0.03

AUDADIS-IV = Alcohol Use Disorder and Associated Disabilities Interview Schedule-IV; BDS = Behavior Dimension Scale; CIDI = Composite International Diagnostic Interview; GHQ-12 = General Health Questionnaire; SCID = Structured Clinical Interview for DSM Disorders; SE = standard error; WMH = World Mental Health.

The meta-analysis revealed that the pooled lifetime prevalence of BD type 1 was 1.06%, 95%CI 0.81-1.31 (Z = 8.28, p < 0.001, number of studies = 20; Q-test = 370.4, p < 0.001, I2 = 95%). The lifetime prevalence of BD type 2 was 1.57%, 95%CI 1.15-1.99 (Z = 7.31, p < 0.001, number of studies = 9; Q-test = 180.26, p < 0.001, I2 = 96%). The pooled 1-year prevalence of BD type 1 was 0.71%, 95%CI 0.56-0.86 (Z = 9.4, p < 0.001, number of studies = 15, Q-test = 75.2, p < 0.001, I2 = 81%). The 1-year prevalence of BD type 2 was 0.50%, 95%CI 0.35-0.64 (Z = 6.7, p < 0.001, number of studies = 8; Q-test = 6.69, I2 = 90%). Sensitivity analysis did not show a significant influence of any individual study on the results of meta-analysis. Visual inspection of a funnel plot did not reveal a significant publication bias for the prevalence of BD type 1 or type 2.

A subgroup analysis dividing the studies according to diagnostic criteria (DSM-III, DSM-IIIR, and DSM-IV) showed a significantly higher lifetime prevalence of BD type 1 according to the DSM-IV criteria compared to the DSM-III and DSM-IIIR criteria (DSM-III: 0.47%, 95%CI 0.23-0.72; DSM-III-R: 1.18%, 95%CI 0.63-1.74; DSM-IV: 1.92%, 95%CI 1.25-2.59; χ2 = 7.34, p < 0.001). There was a marginally significant statistical difference in the lifetime prevalence of BD type 2 according to the diagnostic criteria (DSM-III: 0.92%, 95%CI 0.32-1.51; DSM-IV: 1.65%, 95%CI 1.22-2.09; χ2 = 3.88, p = 0.05).

Discussion

To the best of our knowledge, this is the first meta-analysis of the prevalence of BD to compare different diagnostic criteria in community-based surveys. The mean pooled lifetime prevalence of BD type 1 was 1.1%, while the pooled lifetime prevalence of BD type 2 was 1.2%. As expected, the lifetime prevalence was higher than the 12-month prevalence for both BD types. In an additional subgroup analysis, we found a progressive and significant increase in the lifetime prevalence of BD according to more recent diagnostic criteria. For BD type 1, lifetime prevalence was significantly higher using DSM-IV criteria, followed by DSM-III-R and DSM-III, respectively. Likewise, lifetime prevalence of BD type 2 was higher employing DSM-IV criteria than DSM-III-R criteria.

Our results are similar to those found in a previous systematic review, which found a pooled 1-year prevalence estimate for BD (types 1 and 2) of 0.84%.14 Global regional differences were observed in the prevalence of BD, with higher estimates in North Africa/Middle East compared to other regions, and no effect of economic status of the study country. However, the pooled prevalence estimates were not derived through a meta-analytic approach, thus making it difficult to compare these studies. On the other hand, our study presents some advances, as we also evaluated lifetime prevalence estimates and compared estimates according to diagnostic criteria. This provided a more comprehensive outlook of BD prevalence, of the evolution of population trends, and of how changes in diagnostic criteria influenced estimates of the prevalence of BD.

Since the introduction of the DSM-III in 1980, several important methodological innovations have been introduced in psychiatric epidemiological studies, including structured psychiatric interviews and diagnostic criteria. Despite these innovations and changes in diagnostic criteria over time, the prevalence of BD type 1 has been remarkably consistent over the years, with rates ranging from 0.0 to 1.7% in different studies. Both the Epidemiological Catchment Area Study (ECA) of more than 18,000 participants46 and the National Comorbidity Survey (NCS) of more than 8,000 participants31 in the U.S. reported rates of 0.8 and 1.6%, respectively. Additionally, 14 studies from European countries including more than 29,000 participants reported rates from 0.3% (Iceland) to 1.8 % (Netherlands).47 There is equally persistent evidence that the 12-month prevalence of BD type 1 is slightly lower than the lifetime prevalence, at approximately 1%.

BD type 2 was referred for the first time as a clinical diagnosis in the DSM-III-R, where it was included in the bipolar disorder not otherwise specified category; however, it became an independent diagnostic entity in the DSM-IV. In community-based studies, the prevalence of BD type 2 is generally lower than that of BD type 1, with rates ranging from 0.5 to 3.0% for lifetime8 and 1% for 12-month prevalence.48 Clinical studies have reported a much higher prevalence of BD type 2 compared to community-based studies.9 Possible explanations for this discrepancy are difficulties in recognizing hypomanic episodes due to the shorter duration of symptoms and minimal functional impairment. In addition, the structured diagnostic interviews commonly used in studies have poor specificity for identification of patients with past or current history of BD type 2. Within this context, the absence of information on hypomanic symptoms would lead to misdiagnosis of unipolar depression, thus underestimating the prevalence of BD type 2.48-50

Profound changes have been made to diagnostic criteria for BD in the last 40 years, transforming the theory and practice of mental health. In the DSM-III,11 the term BD replaced the older term manic-depressive illness. Further improvement was made to the BD diagnostic criteria in the DSM-III-R51 by presenting, for the first time, the diagnosis of bipolar disorder not otherwise specified. Finally, the DSM-IV13 converted the BD diagnosis from a single set of criteria to a more nuanced diagnostic system, including two discrete diagnostic entities, BD type 1 and BD type 2.

Although there are no significant differences in the criteria for BD type 1 between DSM-III, DSM-III-R, and DSM-IV, we observed a significant increase in prevalence with the use of the latter. This finding may be explained by the use of different assessment scales and interviews in the studies. Although studies in clinical samples have demonstrated that agreement for a fully structured interview applied by laypersons and for semi-structured interviews applied by clinicians was moderate to excellent,52 in community studies, agreement ranged between poor and fair.53Additionally, there are also differences among structured interviews. Studies using the Composite International Diagnostic Interview (CIDI) interview have yielded prevalence rates of BD type 1 approximately two times higher compared to studies using the Diagnostic Interview Schedule (DIS) interview.16 This discrepancy appeared because the CIDI is an expansion of the DIS, and was developed by an international task force to address the problem that DIS diagnoses are exclusively based on the DSM definitions and criteria.54

In contrast, the criteria for BD type 2 underwent major changes from the DSM-III-R to the DSM-IV. While BD type 2 was categorized as bipolar disorder not otherwise specified in the DSM-III-R, in the DSM-IV it was given its own explicit category. Therefore, the difference in BD type 2 prevalence between DSM-III-R and DSM-IV is possibly attributable to changes in diagnostic criteria rather than to the characteristics of the assessment instruments. Finally, better recognition of BD by psychiatrists may also contribute to the increased prevalence of BD type 1 and type 2 observed in recent years.

The present results should be viewed in light of some limitations. First, despite publication of the DSM-5 in May 2013, no studies using its operational criteria were found for inclusion in the present review. We did not include studies that assessed prevalence of BD in children and adolescent. Several lines of evidence suggest that many BD patients have their first mood episode early in life, which can influence estimates of lifetime prevalence in adults.55We did not include studies of BD spectrum in the present meta-analysis. Despite its relevance, there are differences in definition and operationalization of this construct that preclude its pooled analysis. Future systematic reviews and meta-analyses should address these points to provide a broader estimate of the prevalence of BD over the life course. The studies included in this meta-analysis were significantly heterogeneous. To overcome this possible limitation, we carried out the analysis using random-effects models, which are more appropriate than fixed-effect models when dealing with heterogeneity. Some studies included had poor methodological quality, which may have biased our results. Nonetheless, sensitivity analysis did not significantly change the pooled analyses. Finally, although we conducted a careful search of the literature in different databases, we may have missed some studies, in particular those published in languages other than English and those not yet published.

On the other hand, strengths of this meta-analysis are the inclusion of community and population-based studies from different countries, allowing generalization for the whole population. We covered a long period of publication (1980-2013) and investigated the prevalence of type 1 and type 2 BD in different time frames (i.e., lifetime and 12-month prevalence). Finally, we were able to compare BD prevalence across different operational diagnostic criteria (DSM-III, DSM-III-R, DSM-IV). This analysis showed a steady increase in the prevalence of type 1 and type 2 BD over the years. Overall, these analyses provided a broader view of the prevalence of BD, and its dynamics, in the general population.

In conclusion, this meta-analysis of community-based epidemiological studies confirms that estimations of prevalence of BD type 1 and type 2 are low in the general population. The increase in prevalence from DSM-III and DSM-IIIR to DSM-IV may reflect different factors, such as minor changes in diagnostic operationalization, use of different assessment instruments, or even a genuine increase in the prevalence of BD. Additional studies are necessary to disambiguate these topics and evaluate whether recent changes in the diagnostic criteria for BD in the DSM-5 will lead to changes in prevalence.

Acknowledgements

BSD receives research support from Conselho Nacional de Desenvolvimento CientÍfico e TecnolÓgico (CNPq) and Intramural Grant from Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG, Brazil. JOF receives a scholarship from CNPq. ECC is supported by Programa Nacional de PÓs-Doutorado em Saúde.

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Received: February 24, 2015; Accepted: February 26, 2015

Correspondence: Erico Castro-Costa, Av. Augusto de Lima, 1715, office 610, CEP 30190-002, Belo Horizonte, MG, Brazil. E-mail:castro-costa@cpqrr.fiocruz.br

Disclosure The authors report no conflicts of interest.

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