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?
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?
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 nonclinicians 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?