[Epidemiology and prevention of mental disorders]

From a bibliographic analysis and personal experiences, the authors present the advantages of the epidemiologic method in psychiatry. They point out its specificity and the methodological difficulties. Since the psychiatric practices are being deeply transformed, it becomes essential to know precisely the importance and the distribution of mental diseases in the population. It is not possible to image changing a care system trend without knowing the real needs of the population. The descriptive epidemiologic method contributes to this. The aim of analytic epidemiology is ever more important since it allows to spot the circumstances in which mental diseases appear and are developed, and to elaborate etiological hypotheses. Finally, this favors preventive approaches where evaluative epidemiology permits to measure the validity and effectiveness of programs which, like those elaborated for other social calamities (transmissible diseases, degenerative diseases), take place for studies in the field of mental health disorders.