Statistics in medicine
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Statistics in medicine · Apr 2001
Comparative StudyComparisons of two-part models with competitors.
Two-part models arise when there is a clump of 0 observations in a distribution of continuous non-negative responses. Several methods for comparing two such distributions are available. These include the straightforward application of the z-test (or t-test), the Wilcoxon-Mann-Whitney rank sum test, the Kolmogorov-Smirnov test, and three tests that use a 2 degree of freedom chi(2) test based on the sum of the test for equality of proportions and a conditional chi(2) test for the continuous responses. ⋯ If the reverse holds, the difference in the proportion of zeros reinforces the difference in means and some single-part models (the rank sum or Kolmogorov-Smirnov) do best. In those cases, the two-part models are not far behind, although statistically significantly poorer with respect to power. Published in 2001 by John Wiley & Sons, Ltd.