We have evaluated the power for detecting a common trait determined by two loci, using seven statistics, of which five are implemented in the computer program SimWalk2, and two are implemented in GENEHUNTER. Unlike most previous reports which involve evaluations of the power of allelesharing statistics for a single disease locus, we have used a simulated data set of general pedigrees in which a twolocus disease is segregating and evaluated several nonparametric linkage statistics implemented in the two programs. We found that the power for detecting linkage using the Sall statistic in GENEHUNTER (GH, version 2.1), implemented as statisticE in SimWalk2 (version 2.82), is different in the two. TheP values associated with statisticE output by SimWalk2 are consistently more conservative than those from GENEHUNTER except when the underlying model includes heterogeneity at a level of 50% where theP values output are very comparable. On the other hand, when the thresholds are determined empirically under the null hypothesis, Sall in GENEHUNTER and statisticE have similar power.
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