[Evaluation of the effectiveness of a diagnostic examination: from data to medical decision (author's transl)].

It is desirable to assess the value of special investigations by objective criteria. Conditional probabilities are suitable for this purpose. Sensitivity and specificity indicate the prevalence of a sign in a disease. Predictive values estimate the probability of a disease when a sign is present and the probability of absence of disease when the sign is absent. Comparison between the informational value of a sign or examination with concepts of cost or of risk to the patient is then possible. This made be used as a basis for determining a strategy for special investigations in the establishment of a diagnosis.