Department of Biostatistics Seminar/Workshop Series

Sensitivity, Specificity, and Useful Measures of Diagnostic Utility

Frank E Harrell Jr, PhD

Professor and Chair, Department of Biostatistics, Vanderbilt University School of Medicine

Wednesday, November 30, 1:30-2:30pm, MRBIII Room 1220

Medical diagnostic research, as usually practiced, is prone to bias and even more importantly to yielding information that is not useful to patients or physicians and sometimes overstates the value of diagnostics. Important sources of these problems are conditioning on the wrong statistical information, reversing the flow of time, and categorization of inherently continuous test outputs and disease severity. It will be shown that sensitivity and specificity are not properties of tests in the usual sense of the word, and that they were never natural choices for describing test performance. This implies that ROC curves are unhelpful. So is categorical thinking.

The many advantages of diagnostic risk modeling will be discussed, and this talk will show how pre- and post-test diagnostic models give rise to clinically useful displays of pre-test vs. post-test probabilities that themselves quantify diagnostic utility in a way that is useful to patients, physicians, and diagnostic device makers. And unlike sensitivity and specificity, post-test probabilities are immune to certain biases, including workup bias.