[What is a predictive factor?]

Everyday clinical and therapeutic practice relies on signs, variables or factors allowing to adjust strategies influencing the short and if possible long term evolution of mental disorders. The possible prediction of the future course of illness by such variables is debated. Actually in the present literature a confusion appears between several terms. Stricto sensu the predictive value of a test or of a diagnostic procedure supposes the assessment of a discriminative sensibility and specificity relative to a well established fact: the illness. The importance of some clinical and biological factors may be gauged by such means. More frequently risk factors are proposed. A risk factor represents a particular characteristic or condition associated to an increased probability of a specific disorder being present or developing ulteriorly. However, such factors are not necessarily causal factors. The search of prognostic factors also constitutes an important step in our understanding of pathological processes as well as of evolution.