The Prevalence of Mental Illness How do we know how many people have or have had mental health problems? How do we, as a society, plan for providing mental health services?

How do we measure psychiatric disorders in community samples? Why not just count the number of people receiving treatment for psychiatric disorders? Why not just ask people door to door if they are distressed? Ignores people with problems who are not receiving treatment. Doesn't distinguish betwee people who have significant psychiatric problems from people who don't.

How do we measure psychiatric disorders in community samples? Why not have mental health professionals go door to door and assess people’s mental health? What’s the problem with using questionnaires or interviews done by non-mental health professionals? It's too expensive. It's difficult to decide how to make the "dichotomous decision" about whether people have a psychiatric disorder or don't. There are no medical tests to make diagnoses. Behaviors that may be acceptable in some situations, settings, cultures, are not acceptable in others. Decisions are made based on what is "socially normative" in a given setting.

First steps toward preparing for estimating prevalence of mental illness in the United States President Carter’s Commission on Mental Health and Illness, 1978, identified need to estimate prevalence of mental illness in general population NIMH funded development of the Diagnostic Interview Schedule, a research diagnostic interview that non-clinicians can administer.

First of 2 epidemiological studies Epidemiologic Catchment Area (ECA) Study (published 1991) Interviewed 20,000 people in 5 different communities (New Haven, Baltimore, Durham, St. Louis, Los Angeles) Became main source of data on the U.S. prevalence of mental disorders and use of services to treat these disorders for 1990’s

Weaknesses of ECA Study No studies of reliability and validity of the Diagnostic Interview Schedule completed until after completion of ECA data collection. Reliability and validity studies showed low agreement between DIS results and results of clinical interviews.

Weaknesses (continued) ECA only carried out in 5 locations; therefore could not be generalized to U.S. 5 locations all metropolitan areas that contained large university-based hospitals (therefore tell us little about rural areas or areas without specialty services)

Second of 2 epidemiologic studies National Comorbidity Survey (NCS) (published 1994) Household survey of 8,000 people in age range 15-54 Also sample of students living in group housing Carried out in 174 counties in 34 states (designed to be representative of entire country) Used a modified version of the Diagnostic Interview Schedule, known as the Composite International Diagnostic Interview

Weaknesses of NCS Almost all diagnoses studied were Axis I disorders, and not all Axis I disorders were studied However, the most common Axis I disorders were covered in the study: Mood disorders Anxiety disorders Addictive disorders Non-affective psychoses

Lifetime vs. 12-month prevalence Lifetime prevalence: proportion of people sampled who ever experienced the disorder 12-month prevalence: proportion of people sampled who reported an episode of the disorder within the 12 months prior to the interview

Results of NCS Most common psychiatric disorders? Major depression Lifetime prevalence: 17.1% 12-month prevalence: 10.3% Alcohol dependence Lifetime prevalence: 14.1% 12-month prevalence: 7.2%

Results (continued) Social phobia (an anxiety disorder) Lifetime prevalence: 13.3% 12-month prevalence: 7.9% Simple phobia (an anxiety disorder) Lifetime prevalence: 11.3% 12-month prevalence: 8.8%

Summary results 49.7% of all people sampled reported a lifetime history of at least one psychiatric disorder 30.9% of all people sampled reported having one or more disorders within the 12 months preceding the survey.

Gender differences Men are much more likely to have addictive disorders and anti-social personality disorders than women. Women are much more likely to have mood disorders than men (except for mania, which is equally common among men and women).

Comorbidity Comorbidity=presence of more than one disorder in a single individual. 79% of all the disorders reported by the sample are comorbid disorders. 58.9% 12-month disorders and 89.5% of severe 12-month disorders occurred in 14% of the people sampled. Approximately 3 – 6% of people with 12-month disorders are considered SPMI (severely and persistently mentally ill).

What does this mean? A history of some psychiatric disorder is quite common in the United States (around half of all people have one at some point in their lives). However, the major burden of psychiatric disorder in the United States is carried by a relatively small proportion of the population (1/6).

What does this mean? Important to do research on the prevention of secondary disorders. Epidemiologic information about the prevalence of individual disorders is less important than information on the prevalence of comorbidity, impairment of functioning (disability), and chronicity.

What policy implications can you identify? Where should funding for research be directed? Where should funding for development and maintenance of mental health services be directed?