The use of a two-phase design in a prevalence survey

Abstract

A method is described for the use of a two-phase design in a prevalence survey of non-psychotic psychiatric morbidity. The method consists of screening a population sample, then giving a standardised psychiatric interview to varying proportions of those screened, stratified according to the probability of each respondent's being a case. Prevalence rates can then be calculated by weighting back to the original population. By harnessing together two well-proven instruments, the General Health Questionnaire and the Present State Examination, one can obtain a rigorous and internationally comparable description of morbidity while at the same time efficiently deploying scientific staff in the field.