Comparison of -tests for Univariate and Multivariate Mixed-Effect Models in Genome-Wide Association Mapping.

Genome-wide association mapping (GWA) has been widely applied to a variety of species to identify genomic regions responsible for quantitative traits. The use of multivariate information could enhance the detection power of GWA. Although mixed-effect models are frequently used for GWA, the utility of -tests for multivariate mixed-effect models is not well-recognized. Thus, we compared the -tests for univariate and multivariate mixed-effect models with simulations. The superiority of the multivariate -test over the univariate test varied depending on three parameters: phenotypic correlation between variates (), relative size of quantitative trait locus effects between variates ( ), and missing proportion of phenotypic records ( ). Simulation results showed that, when was low, the multivariate -test outperformed the univariate test as and differ, and as increased, the multivariate -test outperformed as increased. These observations were consistent with results of the analytical evaluation of the -value. When was at the maximum, i.e., when no individual had phenotypic values for multiple variates, as in the case of meta-analysis, the multivariate -test gained more detection power as increased. Although using multivariate information in mixed-effect model contexts did not always ensure more detection power than with univariate tests, the multivariate -test will be a method applied when multivariate data are available because it does not show inflation of signals and could lead to new findings.