title: [Introduction to quantitative semiology].
abstract: Clinicians regularly confront dilemmas when ordering and interpreting diagnostic tests. This paper presents the basic principles necessary for the critical appraisal of articles about diagnostic tests. Basic notions such as sensitivity and specificity are defined. The advantages of using the newer notion of likelihood ratios are underlined. Since all these quantities are estimates of unknown true values, the method for calculating confidence intervals are reported. Finally, the simplified expression of Bayes' theorem based on the use of likelihood ratios is described alongside with a simple nomogram making it possible to calculate posttest probabilities at the bedside.
authors.affiliation: Service d'informatique médicale, Hôpital Broussais, Paris.
authors.forename: G
authors.initials: G
authors.lastname: Chatellier
authors.forename: J
authors.initials: J
authors.lastname: Ménard
authors.forename: P
authors.initials: P
authors.lastname: Degoulet
mesh_terms: D001499:Bayes Theorem; D003933:Diagnosis; D006801:Humans; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D018608:Ultrasonography, Doppler