<P> The prevalence of mental disorders has been studied around the world, providing estimates on how common mental disorders are . Different criteria or thresholds of severity have sometimes been used . </P> <P> National and international figures are typically estimated by large - scale surveys of self - reported symptoms up to the time of assessment; sometimes a figure is calculated for the occurrence of disorder in the week, month or year prior to assessment--a point or period prevalence; sometimes the figure is for a person's lifetime prior to assessment--the so - called lifetime prevalence . </P> <P> Numerous large - scale surveys of the prevalence of mental disorders in adults in the general population have been carried out since the 1980s based on self - reported symptoms assessed by standardized structured interviews, usually carried out over the phone . </P>

What is the most common category of mental disorders found in the united states