[Research on psychotherapies. Methodology]

"Assessment" (of outcome and of factors of outcome) and "psychotherapy" are first defined. Although the aims of these surveys are deeply varying depending on their initiators (therapists or administrations), they share the same objects and the same methodological problems. This common problematic is specific, different from those prevailing for epidemiology or therapeutic trials; it also varies depending on the psychiatric and cultural background (for instance, depending on the side of the ocean). The choice of variables is discussed for objects (patients, families, therapists, institutions), sources (self and hetero-questionnaires) and exploratory levels (from symptoms to subjective quality of life). This leads to the choice of instruments, the interest of open ended questions and specific modalities of responses being emphasized. After a discussion of several methods of outcome assessment, the study of factors of change includes a comparison of the naturalistic and experimental approaches. Although these studies encounter some risks and limitations, they have an obvious clinical interest.