Determining how many people have a mental illness can be difficult, and prevalence estimates vary. While numerous surveys include questions related to mental illness, few provide prevalence estimates of diagnosable mental illness , and fewer still provide national prevalence estimates of diagnosable mental illness. This report briefly describes the methodology and selected findings of three large federally funded surveys that provide national prevalence estimates of diagnosable mental illness : the National Comorbidity Survey Replication (NCS-R), the National Comorbidity Survey Replication Adolescent Supplement (NCS-A), and the National Survey on Drug Use and Health (NSDUH). On the other hand, the NCS-R and the NCS-A provide prevalence estimates for specific disorders, which the NSDUH does not provide. Between February 2001 and April 2003, NCS-R staff conducted in-person interviews with more than 9,000 adults aged 18 or older, drawing the sample from households in the contiguous United States. Analyses of NCS-R data have yielded different prevalence estimates. One analysis of NCS-R data estimated that 26.2% of adults had a mental illness within a 12-month period (hereinafter called 12-month prevalence). Another analysis of NCS-R data estimated the 12-month prevalence of mental illness to be 32.4% among adults; the difference may be attributable to the use of more recent information about the U.S. population in weighting the NCS-R data. Both of these estimates include substance use disorders as mental illness; an analysis of NCS-R data estimated the 12-month prevalence of mental illness excluding substance use disorders to be 24.8% among adults. The estimated 12-month prevalence of serious mental illness among all adults was 5.8%. Between February 2001 and January 2004, NCS-A staff interviewed more than 10,000 adolescents aged 13 to 17, drawing the sample from both schools and households in the coterminous United States. Using NCS-A data, researchers estimated the 12-month prevalence of mental illness to be 40.3% among adolescents. Some have suggested that the current version of the DSM identifies people who should not be considered mentally ill. The estimated 12-month prevalence of serious mental illness among all adolescents was 8.0%. Although the NSDUH collects information related to mental illness (e.g., symptoms of depression) from adolescents aged 12 to 17, it does not produce prevalence estimates of mental illness for that population. According to the 2016 NSDUH, the estimated 12-month prevalence of mental illness excluding substance use disorders is 18.3% of adults (aged 18 or older). According to the 2016 NSDUH, the estimated 12-month prevalence of serious mental illness excluding substance use disorders is 4.2% among adults (aged 18 or older). For example, given the difference in prevalence estimates between any mental illness and serious mental illness among adolescents, might policymakers choose to focus on a large group of adolescents that includes many whose mental illnesses may be mild and even transient, or might they choose to focus more narrowly on adolescents with serious mental illness? Policymakers may come to different conclusions about the best policy approach depending in part on how they answer such questions.
Determining how many people have a mental illness can be difficult, and prevalence estimates vary. While numerous surveys include questions related to mental illness, few provide prevalence estimates of diagnosable mental illness (e.g., major depressive disorder as opposed to feeling depressed, or generalized anxiety disorder as opposed to feeling anxious), and fewer still provide national prevalence estimates of diagnosable mental illness. This report briefly describes the methodology and results of three large surveys (funded in whole or in part by the U.S. Department of Health and Human Services) that provide national prevalence estimates of diagnosable mental illness: the National Comorbidity Survey Replication (NCS-R), the National Comorbidity Survey Replication Adolescent Supplement (NCS-A), and the National Survey on Drug Use and Health (NSDUH). The NCS-R and the NCS-A have the advantage of identifying specific mental illnesses, but they are more than a decade old. The NSDUH does not identify specific mental illnesses, but it has the advantage of being conducted annually.
Between February 2001 and April 2003, NCS-R staff interviewed more than 9,000 adults aged 18 or older. Analyses of NCS-R data have yielded different prevalence estimates. One analysis of NCS-R data estimated that 26.2% of adults had a mental illness within a 12-month period (hereinafter called 12-month prevalence). Another analysis of NCS-R data estimated the 12-month prevalence of mental illness to be 32.4% among adults. A third analysis of NCS-R data estimated the 12-month prevalence of mental illness excluding substance use disorders to be 24.8% among adults. The 12-month prevalence of serious mental illness was estimated to be 5.8% among adults, based on NCS-R data.
Between February 2001 and January 2004, NCS-A staff interviewed more than 10,000 adolescents aged 13 to 17. Using NCS-A data, researchers estimated the 12-month prevalence of mental illness to be 40.3% among adolescents. Some have suggested that the current approach to diagnosing mental illness identifies people who should not be considered mentally ill. The 12-month prevalence of serious mental illness was estimated to be 8.0% among adolescents, based on NCS-A data.
The NSDUH is an annual survey of approximately 68,000 adults and adolescents aged 12 years or older in the United States. According to the 2016 NSDUH, the estimated 12-month prevalence of mental illness excluding substance use disorders was 18.3% among adults aged 18 or older. The estimated 12-month prevalence of serious mental illness (excluding substance use disorders) was 4.2% among adults. Although the NSDUH collects information related to mental illness (e.g., symptoms of depression) from adolescents aged 12 to 17, it does not produce estimates of mental illness for that population.
The prevalence estimates discussed in this report may raise questions for Congress. Should federal mental health policy focus on adults or adolescents with any mental illness (including some whose mental illnesses may be mild and even transient) or on those with serious mental illness? Should substance use disorders be addressed through the same policies as other mental illnesses? Members of Congress may approach mental health policy differently depending in part on how they answer such questions.