The concept of evidence-based practice (EBP) springs from the world of public health and epidemiology, which examines the way diseases affect entire populations and considers cost-effective ways to maximize health for the greatest number of people. Recent evidence on the prevalence of mental disorders suggests ways for psychologists to pursue their EBP agenda--both to demonstrate widespread needs and to tailor treatments more effectively, say psychologists with expertise in the area.

The data, from the two largest national and international prevalence studies of mental disorders, find that 26.2 percent of Americans had some kind of diagnosable mental disorder in the past year, while 16.2 percent will suffer from major depressive disorder (MDD) some time during their life. Moreover, many people with these conditions receive inadequate to no treatment, notes the studies' lead author, Harvard University public health policy expert Ronald C. Kessler, PhD. The national data, which reported on MDD prevalence in the United States, appeared in the June 18, 2003 Journal of the American Medical Association (Vol. 289, No. 23), while the international data on a range of mental disorders, including in the United States, appeared in the June 2, 2004 JAMA (Vol. 291, No. 21).

When viewed through the lens of EBP, such findings suggest ways of tailoring interventions in more creative and cost-effective ways to better serve the scope of people who need them, says Jalie A. Tucker, PhD, outgoing chair of APA's Board of Professional Affairs and an expert on substance abuse and the utilization of behavioral health services at the University of Alabama at Birmingham.

For example, about a third of mental disorders in this country are mild, the data find, so the most cost-effective approach for such clients may not be long-term therapy but rather brief problem-focused sessions that highlight motivation for change, risk factors and preventive measures, Tucker says.

The international findings on a broad range of mental disorders--considered preliminary results--examined clinical severity, functioning and service use in a community sample of 60,463 adults in 14 countries. The national data on MDD, part of a replication of the original National Comorbidity Survey on mental disorders in the United States conducted from 1990 to 1992, examined these same factors in a representative sample of 9,090 U.S. adults.

Geoffrey M. Reed, PhD, assistant executive director for professional development in APA's Practice Directorate, says that, taken together, these data overwhelmingly show large numbers of people with mental illness going untreated. To add to the problem, 1999 data from the U.S. Public Health Service find that most people with behavioral health problems delay or avoid seeking help--and when they do get it, they often face a fragmented service-delivery system. "A broader view of the evidence suggests that more services should be provided rather than less," Reed says.

Kessler's data also imply the importance of a "continuum of care" model, which lets clients access appropriate services based on need as their problems improve or get worse over time, Tucker says. In an article reported in the November 2003 Archives of General Psychiatry (Vol. 60, No. 11), Kessler and colleagues found that people who reported mild mental illnesses in the original National Comorbidity Study and lacked sufficient treatment were two to three times more likely than those with no mental illness to have severe outcomes such as suicide, hospitalization and severe mental illness a decade later.

Psychologists could use such data in an evidence-based sense to ask, "What can we do upstream to prevent bigger problems from occurring later on?" Kessler says. "The data suggest we should be treating young people with mild problems early on--just as cardiologists have learned to do with high cholesterol levels," he notes.