Rationale and Objectives. Observer performance studies sometimes use t
oo few cases for estimating diagnostic accuracy from binormal receiver
operating characteristic (ROC) curves, One important problem is degen
erate data sets. We compared a new algorithm, RSCORE4, with the exact-
solution approach to degeneracy in ROCFIT and with the Wilcoxon statis
tic. Methods. Degenerate ROC solutions result from empty cells in the
data matrix. We addressed this problem by adding a small constant to e
mpty cells in a maximum-likelihood program, RSCORE4, When this method
failed, the program branched to a pattern-search algorithm. We tested
the program in a series of Monte Carlo studies. Results. RSCORE4 conve
rged to nondegenerate solutions in every case and gave results closer
to population values than ROCFIT or Wilcoxon. ROCFIT converged to exac
t-fit degenerate solutions, those with zero or infinite parameter valu
es, in more than 40% of the samples. The Wilcoxon statistic was biased
. Conclusion. RSCORE4 seems to outperform other currently recommended
methods for dealing with degeneracy.