Purpose: Area under a receiver operating characteristic (ROC) curve (Az) is widely used as an index of diagnostic performance. However, Az is not a meaningful summary of clinical diagnostic performance when high sensitivity must be maintained clinically. The authors developed a new ROC partial area index, which measures clinical diagnostic performance more meaningfully in such situations, to summarize an ROC curve in only a high-sensitivity region.
Materials and methods: The mathematical formation of the partial area index was derived from the conventional binormal model. Statistical tests of apparent differences in this index were formulated analogous to that of Az. One common statistical test involving the partial area index was validated by computer simulations under realistic conditions.
Results: An example in mammography illustrates a situation in which the partial area index is more meaningful than Az in measuring clinical diagnostic performance.
Conclusion: The partial area index can be used as a more meaningful alternative to the conventional Az index for highly sensitive diagnostic tests.