Measuring the reliability of clinical data: the case for using three observers.

Misclassification of clinical data occurs commonly, because of measurement or judgmental errors, or because of bias in the observational method. The sensitivity and specificity of a given observer (or method) may sometimes be estimated by comparison with an independent "definitive" diagnosis; this is not routinely practical, however, if the "definitive" method involves additional risk or cost. A second possibility is to compare two independent, …