Methodological analysis demonstrates optimal resource allocation for two-phase prevalence surveys of rare disorders, indicating that efficiency depends on relative screening costs and test accuracy.
Two-phase medical surveys, in which a large sample is assessed with an inexpensive screening instrument and a subsample is selected for a more thorough diagnostic evaluation, appear to have great merit in the epidemiologic study of certain rare disorders. We present the optimal design of two-phase surveys when resources are fixed and when 100% of those screened positive in the first phase must be included in the second-phase evaluation. We go on to examine the relative efficiency of this two-phase design compared to a single-phase design in which all resources are used in a survey that employs the diagnostic evaluation. Given information on the accuracy of the screen and the prevalence of the disorder, the utility of the two-phase design depends on the relative cost of the screening to the diagnostic assessments.
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Shrout et al. (1989) studied this question.
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