Abstract
When a confirmatory test is completely accurate or has known low error rates, the sensitivity and the specificity of a screening test can be estimated. When the error rates for the confirmatory test are unknown, Hui and Walter (2) presented a method for estimating the sensitivity and specificity of both the screening and the confirmatory tests using the tests on two populations with different prevalence rates of the infection. The method requires that the tests have equal error rates in the two populations. When this requirement is not met, we show that the estimated prevalence rates are robust when the difference in the prevalence rates of the two subpopulations is large. An alternative design, requiring only one population, but other assumptions, is also described.
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