Predictive values and over-treatment ratio for each algorithm, at three different prevalence levels.

†Assumed stage 1 to stage 2 ratio of two. Note that a ratio of 0.5 would result in almost identical estimates (data not shown), since the differences in sensitivity between stage 1 and 2 are small and have limited influence on the PPV and NPV calculations given the low prevalence of HAT true positives.‡Assuming sensitivity and specificity without suspect follow-up, as done in practice.¶CTC values in parentheses.