Wittkowski transmission disequilibrium test
INFO=<ID=TDT,Number=A,Type=Float,Description="Test statistic from Wittkowski transmission disequilibrium test.">
This annotation indicates the presence of a genetic linkage between a genetic marker and a genetic trait.
The calculation is based on the derivation described in http://en.wikipedia.org/wiki/Transmission_disequilibrium_test#A_modified_version_of_the_TDT.