The fanny algorithm, with the number of clusters pre-selected to be two, resulted in two average silhouette values of 0.6259 and 0.6257 for the AAs and EAs, respectively, implying that the clustering patterns were very similar in the two population groups; subjects were clustered with modest similarity, on average, within the cluster each subject belonged to, compared to the other cluster. Mean (SD) of the cluster membership coefficients are 0.5014 (0.3370) in AAs and 0.5001 (0.3364) in EAs. The means are close to the theoretical 0.5 due to the constraint of summation to one for two clusters. For AAs, there are 475 subjects in one cluster, and 477 in the other. For EAs, subjects were equally clustered with 403 subjects in each cluster. The two clusters that incorporated the first two principal components of the five SDs explained 60.8% and 60.5% of the total phenotypic variation for AAs and EAs, respectively. The membership coefficient was used as a quantitative trait in the subsequent linkage analysis (Fig. 2).
