Significance was determined by permutation testing. Affection status coupled with its covariate values was permuted within families generating 1,000 replicates, and single-point linkage analysis was performed on the observed data and on each replicate. The p-value of a test statistic was calculated as the proportion of permutations whose statistic was equal to or greater than the observed value. Two types of statistics were computed. The first was a LOD score for each marker. The second was the sum of LOD scores across all markers, selected to simultaneously capture multiple regions of significant linkage evidence. Because the statistics were compared to their reference permutation distribution in the calculation of the p-values for each method, the relative proportion of significant tests between methods is an indication of relative power.
