survey as 'unknown' and excluded them from the analysis. Skewness and kurtosis for the self-reported average number of cigarettes smoked per day were 1.38 and 5.11, respectively. To minimize the impact of skewness on linkage analysis results, we transformed the non-zero smoking rates to a natural log-scale prior to linkage analysis (called log-transformed SR). Skewness and kurtosis for this log-transformed smoking rate (including the zeros) became 0.31 and 1.30, respectively. Additionally, we generated a third data set for smoking rate (called categorized SR) in which individuals who smoked 0, 1–5, 6–15, 16–25, 26–35, and greater than 35 cigarettes per day were assigned the values 0, 1, 2, 3, 4, and 5, respectively. Skewness and kurtosis for the categorized SR were 0.58 and 1.88, respectively.
