Age of onset and cumulative risk of mental disorders: a cross-national analysis of population surveys from 29 countries

This study was an observational analysis, meaning it did not test an intervention or compare different treatments. Instead, it investigated the natural patterns of mental disorders across the lifespan in a large global population. The researchers aimed to provide updated and improved estimates for:

**Age of onset:** When mental disorders typically first emerge.

**Lifetime prevalence:** The proportion of people who have experienced a mental disorder at any point in their lives up to the time of the survey.

**Morbid risk:** The cumulative probability of developing a mental disorder by a specific age (in this case, age 75).

The study focused on 13 specific mental disorders as defined by the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) criteria. While the abstract doesn't list all 13, it specifically mentions "alcohol use disorder," "major depressive disorder," and "specific phobia" as the most prevalent.

The study included a very large and diverse sample:

**Sample size:** 156,331 individual respondents.

**Population:** Adults aged 18 years or older, drawn from the general population.

**Sex distribution:** 85,308 (54.5%) female respondents and 71,023 (45.4%) male respondents.

**Geographic scope:** Data was collected from 32 surveys conducted in 29 different countries. This included a mix of economic settings: 12 low-income and middle-income countries, and 17 high-income countries.

**Setting:** These were community epidemiological surveys, meaning participants were recruited from the general population, not from clinical settings.

**Exclusions/Limitations:** The study explicitly states that ethnicity was not assessed, which means the findings cannot speak to potential differences in risk or onset patterns across different ethnic groups.

The researchers used a standardized diagnostic tool called the **WHO Composite International Diagnostic Interview (CIDI)**.

**Instrument:** The CIDI is a fully structured psychiatric diagnostic interview. This means it follows a strict script and set of questions to assess symptoms and diagnostic criteria, aiming for consistency across different interviewers and countries.

**Method:** The interviews were conducted face-to-face. Trained interviewers administered the CIDI to each respondent.

**What it assesses:**

* **Age of onset:** For each mental disorder identified, respondents were asked when their symptoms first began or when they first met the diagnostic criteria. This relies on retrospective recall.

* **Lifetime prevalence:** Based on the responses, the CIDI determines if a person has ever met the criteria for any of the 13 DSM-IV mental disorders at any point in their life up to the time of the interview.

* **Morbid risk:** This is a statistical calculation based on the age of onset data, estimating the cumulative probability of developing a disorder by a certain age (up to 75 years in this study).

**Diagnostic Criteria:** The study used the criteria from the DSM-IV, which was the standard diagnostic manual at the time many of these surveys were conducted.

This study employed a **cross-national analysis of coordinated cross-sectional, face-to-face community epidemiological surveys**, specifically the World Mental Health surveys. This design is observational, meaning researchers observed existing patterns and relationships rather than manipulating variables or assigning participants to intervention groups.

**How they ran the study:**

1. **Data Collection:** Between 2001 and 2022, trained interviewers administered the WHO Composite International Diagnostic Interview (CIDI) to adults aged 18 or older in their communities across 29 countries. Each survey was "cross-sectional," meaning it captured a snapshot of each individual's mental health history at a single point in time.

2. **Standardization:** The use of the CIDI, a "fully structured psychiatric diagnostic interview," is critical. This ensures that the same questions and diagnostic rules were applied consistently across different countries and interviewers, which is essential for comparing data internationally.

3. **Sampling and Weighting:** The surveys were "geographically clustered." This means that instead of randomly selecting individuals from an entire country, researchers might have selected specific regions or neighborhoods and then sampled individuals within those areas. To ensure the results accurately represent the broader population, the data was "weighted to adjust for selection probability." This statistical adjustment accounts for the fact that some individuals or groups might have been more