The dot plot. A starting point for evaluating test performance.

We suggest that evaluations of diagnostic tests start with dot plots that depict multiple test results over multiple clinical states. From this starting point we can calculate posttest probabilities for multiple clinical states at multiple test results. Also, we can project one subset of clinical states as "disease positive" and a second subset as "disease negative" to provide standard analyses such as likelihood ratios, relative operating characteristic curves, posttest/pretest probability plots, sensitivity, specificity, and predictive value. Finally, this starting point provides an excellent basis for comparing multiple studies of diagnostic performance. The advantages of dot plots are illustrated with data on serum ferritin levels over multiple clinical states.