The affection status was coded as 1 for affected and 0 for unaffected. This logistic regression was performed in STATA (v8.2) [14] on the entire dataset, and the predicted value of the probability of affection for each individual was used as the individual's PS corresponding to the set of observed underlying covariates. The presence of measured covariates on both affected and unaffected individuals is required, although only affected individuals are used in the linkage analysis itself.
