The bootstrapping procedure is designed for independent observations and needed to be adapted to the presence of sibs and of multiple observations for each individual. It was decided to resample individuals, not observations. Individuals were selected with replacement from the dataset and each individual in the dataset was assigned the number of times she was picked in the selection procedure. In the interests of simplicity, the bootstrapping calculation repeated the actual data calculation with the full sample, including the adjustments for sibship and multiple observations for the same subject, but at the point when the regression calculations were carried out (i.e., the call to the Matlab procedure glmfit()), the weights assigned to each observation based on their distance from the central age were modified by being multiplied by the number of times the subject was included in the selection procedure. This was intended to preserve the overall character of the sibship alteration of weights, since if an individual was included in the sample multiple times, it was not considered desirable to count her as her own sib. Similarly, the multiplicity
