[Methodology in psychiatric epidemiologic research].

Crucial epidemiological variables are described: incidence, prevalence, and relative risk. Of primary importance to comparison of rates of illness and testing hypotheses as to its causes and course are the exact identification and definition of mental disorders. In recent years a variety of screening instruments for assessing both general mental impairment and specific mental disorders have been developed. The methodological standards demanded of a good screening instrument are discussed, namely, the identification of all actual cases of illness (as far as possible) without too many false positive findings among the healthy persons examined.