[Mental disorders in children: the value of epidemiology].

Epidemiological research on the mental health of children is not well developed in France, as demonstrated by the very small number of publications on the subject, especially in French. The purpose of this article is to show the contribution of epidemiology to an understanding of childhood mental illness. We emphasize descriptive epidemiology (currently the most developed component), but discuss analytic and evaluative epidemiology as well. We have thus considered methodological issues related to the advantages and limitations of techniques employed, using concrete examples from international publications. For example, an extensive review of the literature reveals considerable disparity in figures on the prevalence of psychiatric disorders, chiefly because of problems of variation in definitions used and in the places and techniques of data collection (especially screening tools and diagnostic classifications). Only studies carried out in representative samples of the general population allow reliable evaluation of frequency, but these are particularly difficult and costly. The same may be said for follow-up studies, in particular those on birth cohorts, whose principle importance is that they enable the identification of predictive factors for mental disorders, starting from earliest childhood. Entire areas are currently in need of development, such as the genetic epidemiology in mental illness, clinical trials, or the evaluation of programs. Epidemiology enables the evaluation of service needs, the identification of 'risk groups' and a scientific approach to explanatory factors. In a country such as France where nearly all children are in the school system from the age of 3 years on, schools should become a place for early detection, which assumes a considerable increase in the means available and an innovative policy in the training of health personnel, especially in the area of mental health.