DURHAM, N.C., Sept. 15 (UPI) -- The prevalence of anxiety, depression and substance dependency may be about twice as high as the mental health community has thought, U.S. researchers say.
Duke University psychologists Terrie Moffitt and Avshalom Caspi and colleagues from the United Kingdom and New Zealand used data from a long-term study of more than 1,000 New Zealanders from birth to age 32.
The researchers say people vastly underreport the amount of mental illness they've suffered when asked to recall their history years after the fact, but self-reporting from memory is the basis of much of what is known about the prevalence of anxiety, depression, alcohol dependence and marijuana dependence.
Longitudinal studies like the study in New Zealand that track people over time are rare and expensive, Moffitt says.
"If you start with a group of children and follow them their whole lives, sooner or later almost everybody will experience one of these disorders," Moffitt, the Knut Schmitt-Nielsen professor of psychology and neuroscience at Duke University, said in a statement.
Moffitt and Caspi's findings from the Dunedin Study, published in the journal Psychological Medicine, found 41 percent of those ages 18-32 had experienced clinically significant depression and the rate of alcohol dependence for those ages 18-32 was 32 percent.