Psychiatric morbidity in primary public health care: a Nordic multicentre investigation. Part I: method and prevalence of psychiatric morbidity.

The prevalence of mental illness in five different Scandinavian primary care populations was investigated in this study. Patients consecutively consulting their general practitioner a particular week-day were included in the study. Initially the SCL-25 was applied and next the high scores and a sample of the low scores were interviewed by the PSE. In the analysis the screening procedure was first validated. The internal validity of the SCL was tested by means of Rasch latent structure analysis and the external validity tested by ROC/QROC analysis. Based on this, a short 8-item version of the SCL was developed. The prevalence of mental illness in all centres was 0.26 with a minimum of 0.14 in Nacka and a maximum of 0.34 in Turku.