Review Paper

Prevalence and Incidence Studies of Anxiety Disorders: A Systematic Review of the Literature

Julian M Somers, MSc, PhD¹, Elliot M Goldner, MHSc, MD², Paul Waraich, MHSc, MD¹, Lorena Hsu, MSc³

Objective: To present the results of a systematic review of literature published between 1980 and 2004 reporting findings of the prevalence and incidence of anxiety disorders in the general population. Method: A literature search of epidemiologic studies of anxiety disorders was conducted, using MEDLINE and HealthSTAR databases, canvassing English-language publications. Eligible publications were restricted to studies that examined age ranges covering the adult population. A set of predetermined inclusion and exclusion criteria were used to identify relevant studies. Prevalence and incidence data were extracted and analyzed for heterogeneity. Results: A total of 41 prevalence and 5 incidence studies met eligibility criteria. We found heterogeneity across 1-year and lifetime prevalence rates of all anxiety disorder categories. Pooled 1-year and lifetime prevalence rates for total anxiety disorders were 10.6% and 16.6%. Pooled rates for individual disorders varied widely. Women had generally higher prevalence rates across all anxiety disorder categories, compared with men, but the magnitude of this difference varied. Conclusion: The international prevalence of anxiety disorders varies greatly between published epidemiologic reports. The variability associated with all anxiety disorders is considerably smaller than the variability associated with individual disorders.Women report higher rates of anxiety disorders than men. Several factors were found to be associated with heterogeneity among rates, including diagnostic criteria, diagnostic instrument, sample size, country studied, and response rate. (Can J Psychiatry 2006;51:100–113) Click here for author affiliations.  Click here for information on funding and support.  Clinical Implications Significant heterogeneity in the prevalence of anxiety disorders signals the need for population-specific health policies and planning. The prevalence of anxiety disorders eclipses the capacity of specialized mental health services. Anxiety disorders remain prevalent throughout ages 18 to 64 years. Limitations The observed heterogeneity may be related to environmental or cultural factors associated with the location of each contributing investigation. Variance owing to methods of diagnosis and measurement account for a limited portion of the observed heterogeneity. An insufficient number of incidence studies are available to clarify details concerning the onset of symptoms. Key Words: anxiety disorders, panic disorder, phobia, obsessive–compulsive disorder, posttraumatic stress disorder, generalized anxiety disorder, prevalence, incidence, systematic review Résumé : Études de la prévalence et de l’incidence des troubles anxieux : une étude systématique de la littérature

In recent years, it has been increasingly acknowledged not only that anxiety disorders are highly prevalent, but also that the burden of illness associated with these disorders is often considerable. A broad understanding of the etiology of anxiety includes a multiplicity of factors, such as biological, psychological, and social determinants, which are mediated by a range of risk and protective factors. Cross-cultural studies in epidemiology are a critical source of information regarding the interplay between these factors. Effective forms of intervention are available and are the subject of ongoing research, but it is an immense public health challenge to coordinate the delivery of these programs and services. Studies in comparative epidemiology play a vital role in the development of health policy concerning anxiety. Empirical knowledge of regional prevalence is fundamental to understanding the relative demand for services. Such knowledge is also necessary to identify the most appropriate avenues for intervention.

The present review, which is the fifth in a series of papers that will present systematic reviews of the prevalence and incidence of psychiatric disorders drawn from studies published in the English literature in the years 1980 to 2004, sought to synthesize international research on this topic. Results and observed patterns of heterogeneity are discussed in relation to health services planning as well as implications for additional research.

Methods

The methods employed in this review have been presented in more detail elsewhere (1). The MEDLINE and HealthSTAR databases were searched for relevant studies; the key indexing terms epidemiology, prevalence, and incidence were used, combined with the search terms mental disorders, anxiety disorders, panic disorder, phobia, obsessive–compulsive disorder, posttraumatic stress disorder, and generalized anxiety disorder. The search was limited to English-language studies published between 1980 and 2004. Reference lists of relevant primary and review articles identified were also searched.

Prevalence and incidence studies were eligible for inclusion if they were community surveys using probability sampling techniques. Eligible publications were restricted to studies having sample sizes of 450 people or more that examined age ranges covering the adult population. Only studies using current diagnostic criteria and case identification based on either standardized instruments or clinician diagnosis were included. Prevalence and incidence data, including overall, sex-specific and age-specific rates, were extracted from eligible studies.

Qualitative analyses of variables related to methodology were conducted to summarize and elucidate any observed differences between rates. Each set of rates was also pooled according to a Bayesian approach to metaanalysis; the Fastpro software program was used. Readers interested in a more detailed discussion of this approach should refer to Eddy and others (2). Each of the pooled rates was analyzed for heterogeneity with chi-square tests according to the Fleiss method (3).

Results

Description of Studies

From the citations and abstracts generated by the initial electronic search, we identified 80 prevalence and 10 incidence studies potentially meeting inclusion criteria, in addition to 28 review papers (4–31). The full texts of these articles were retrieved. We searched all reference lists of identified studies and reviews, generating an additional 38 prevalence and 6 incidence studies for which full-text articles were obtained.

Of the 118 prevalence studies for which full-text articles were reviewed, 71 prevalence papers of anxiety disorders met eligibility criteria (32–95,96–102), resulting in a total of 41 unique primary investigations of anxiety disorders included in this review. We excluded a total of 47 studies: 35 studies did not meet eligibility criteria, and 12 presented duplicate data. Of the 16 incidence studies identified, 11 were excluded, 8 did not meet inclusion criteria, and 3 were based on duplicate study samples. This resulted in 5 incidence studies of anxiety disorders that could be included (54,90,103–105). Most studies meeting inclusion criteria used nonhierarchical diagnostic approaches. Predictably, the few studies using hierarchical diagnoses reported relatively lower rates of individual disorders.

Prevalence Studies

Findings, for the 34 papers reporting overall and (or) sex-specific 1-year and (or) lifetime prevalence rates for panic disorder, agoraphobia, social phobia, specific phobia, OCD, PTSD, GAD, and TAD, are presented in Tables 1 to 3. Age-specific lifetime prevalence rates for these disorders are also presented in Figure 1 (33,34,40,44,59,66,73,81, 84,94,101,106). The results of studies reporting only data for point prevalence or 6-month prevalence are not presented (36,37,41,45,49,53,54, 56,6,63,67,69,70,74–76,78,86,87, 92,93,107). Analysis of data was carried out only when 3 or more rates were reported as this was the minimum number of values required to produce pooled rates.