The (in)validity of sensitivity and specificity

This paper is a legacy of the first author, and after her untimely death reconstructed by the second author as a tribute to Irene Guggenmoos's contribution to biostatistics. It discusses two different views on diagnostic testing: the classical view in which sensitivity and specificity of a diagnostic test are considered universal constants, and the more statistical point of view that focuses on predictive values. The differences between the two paradigms are outlined and practical examples are discussed to show that the familiar concepts of sensitivity and specificity must be handled with care and not used indiscriminately.