Wikipedia
W-test
In statistics, the W-test is designed to test the distributional differences between cases and controls for categorical variable set, which can be a single SNP, SNP-SNP, or SNP-environment pairs. It takes a combined log of odds ratio form, calculated from the contingency table of the variable set. The test inherits a chi-squared distribution with data-set adaptive degrees of freedom f, estimated from smaller bootstrapped samples of the data. The flexible and data-corrected probability distribution allows W-test to give relatively accurate p-values under complex genetic architectures.