title: [Grand types of studies 2: analytical studies].
abstract: OBJECTIVE
  This paper describes the hierarchy of analytical studies, from the observational studies to the experimental ones.
  
  
  METHODS
  Case-control studies, the most frequently performed among analytical studies, may generate or confirm hypotheses. They are of particular use for rare diseases. Cohort studies aim mainly at confirming hypotheses already tested, and at precisely quantifying the magnitude of effect. Randomisation aims at the elimination of confounding factors, and meta-analysis, at decreasing potential selection biases and increasing power. Those goals may not always be achieved. PERSPECTIVES AND PROJETS: The study power, or the beta error, are major factors to be determined when designing a study, before any attempt of realization.
authors.affiliation: Service de Médecine Interne et RECIF-Amiens (Réseau d'Epidémiologie International Francophone), CHU Nord, place Victor-Pauchet, 80054 Amiens cedex 01, France. duhaut.pierre@chu-amiens.fr
authors.forename: P
authors.initials: P
authors.lastname: Duhaut
authors.forename: L
authors.initials: L
authors.lastname: Le Page
authors.forename: D
authors.initials: D
authors.lastname: Boutin
authors.forename: J P
authors.initials: JP
authors.lastname: Ducroix
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D004311:Double-Blind Method; D006801:Humans; D015201:Meta-Analysis as Topic; D016032:Randomized Controlled Trials as Topic