for the ALDX1 phenotype for alcoholism. For the ALDX2 phenotype, this yielded 117 affected sib pairs with their parents for a total of 468 individuals. We utilized MAPMAKER/SIBS linkage program [6] to estimate the full multipoint probability of each pair of selected sibs sharing 0, 1, or 2 alleles identical by descent (IBD) on each chromosome. We obtained the Kaplan-Meier curves as the approximation to the baseline functions using the available age-of-onset data from all of the founders in the full dataset (287 for ALDX1 and 289 for ALDX2). The founders are individuals who do not have parents in pedigree and are considered as random subjects from the general population. The Kaplan-Meier survival curves for females and males (figures not shown here) indicate strong evidence of sex differences in ages of onset distributions. Alcohol dependence is more common in males than females. The Kaplan-Meier survival curves for smokers and nonsmokers (figures not shown here) also indicate distributional differences between smokers and nonsmokers.
