Mental health disorders can take a serious toll on all that is life—affecting not only personal well-being, but also relationships and school or job performance. According to the National Institute of Mental Health, an estimated 20% of American adults are affected by a mental disorder during any given year. Other organizations place this figure higher, at closer to 30%.

Many people who suffer from a mental disorder do not seek treatment, but experts speculate that this may not be a major problem since many of these cases may be mild in severity. However when more severe, mental disorders can lead to disability—in fact, mental disorders make up four of the top ten causes of disability in the US and other developed countries.

A new study in the June 2005 issue of the Archives of General Psychiatry set out to obtain more accurate data on the prevalence and severity of the most common mental disorders. The findings suggest that just over 25% of American adults have mental disorders in any given year, and that the severity of these mental disorders is mild or moderate for the majority.

About the Study

Between February 2001 and April 2003 researchers from Harvard conducted a national face-to-face survey of a representative sample of American households. The researchers interviewed 9,282 English-speaking adults age 18 and older using the World Health Organization World Mental Health Survey Initiative version of the Composite International Diagnostic Interview.

The survey looked at the four most common types of mental disorders (as defined in the Diagnostic and Statistical Manual, 4th Edition, or DSM-IV, commonly used by psychiatrists):

Based on the survey answers, the researchers classified an individual’s disorder as serious (e.g., suicide attempt, work disability, or bipolar disorder), moderate (e.g., suicide gesture or plan, substance dependence without serious impairment, moderate work limitation), or mild.

The Findings

Approximately one out of four adults surveyed (26.2%) had symptoms consistent with a diagnosable mental disorder. Most had disorders that were mild (40.4%), followed by moderate (37.3%), and serious (22.3%).

Anxiety disorders were the most common type, followed by mood, impulse control, and then substance abuse. The most prevalent disorders were specific phobias, social phobias, and major depressive disorders. Mood disorders were the most likely to be classified as serious, while anxiety disorders were the least likely. In general, the more disorders an individual had, the more likely they were to be serious.

The authors point out a few limitations in applying these results to the general population. First, they interviewed only adults in English-speaking households, leaving out non-English speakers, as well as those who are homeless or in institutions. Second, they did not look at all DSM-IV diagnoses—for instance, schizophrenia was not included. Finally, because people may be embarrassed to talk about their emotional and personal behaviors, it is likely that this study underreported the total prevalence of mental disorders.

How Does This Affect You?

This study suggests that mental health disorders are common in the United States, affecting more than one out of four Americans at any one time. Additionally, it showed that while most people may suffer from mild forms of mental disorders, a significant proportion of the population has mental disorders that are moderate or severe enough to materially affect their quality of life.

Another study, by the same group of authors and also in this issue of the Archives of General Psychiatry , found that one out of two Americans would qualify for a diagnosis of a mental disorder over the course of their lifetime. These results should be viewed with some skepticism since no other diagnoses in any branch of medicine occurs with nearly such a high frequency. Interestingly, however, this study found that the average age of onset varies widely among the disorders—anxiety and impulse disorders were most likely to start around the age of 11, substance abuse at age 20, and mood disorders at age 30.

These findings underscore the importance of adequate mental health screening and treatment in the US. All of these disorders are treatable; some of them quite effectively. Still, many people do not get help due to the stigma they feel is attached to emotional problems. These studies, however, clearly show that people with mental disorders are hardly alone.