# Changes

$\mathbf{Q}=\mathbf{{U_{meta}}^T}\mathbf{W}\mathbf{U_{meta}}$, where $\mathbf{W}$ is the diagonal matrix of weights of rare variants included in a gene.
As shown in [http://www.ncbi.nlm.nih.gov/pubmed/21737059 '''Wu et. al'''], the null distribution of the $\mathbf{Q}$ statistic follows a mixture chi-sqaured distribution described as