The exdat data set is list of three objects. exdat$Y is a vector of length
1000, 500 0s and 500 1s. exdat$X is a matrix of 1000 by 10. This
simulated X matrix is assumed to be rare variants. All
eliments are 0, 1 or 2. exdat$SNP0indx is a vector of length 10. The
values are 1 or 0, 0 indicate corresponding column of X matrix have no
association with Y vector.