To obtain allowing for selection of markers, note that the regression of on has the same coefficient regardless of selection on . For non-null markers this coefficient isand the covariance is this coefficient times the conditional variance of given in equation 9. For null markers the covariance is zero, so the total covariance isThis expression is substituted into equations 2–5 together with the variance in equation 10 to obtain the power and accuracy of the polygenic score when markers are selected into the score based on their P-values.
