Response rates for the sibling pairs subsample have been higher than for the overall Add Health cohort at each wave because sibling pairs are easier to locate (i.e., with more family contacts) and Add Health has placed priority on maintaining this sample for longitudinal research. Table 2 shows the number of completed in-home interviews for sibling pairs according to their genetic relatedness and their response rates across waves. Response rates are based on individuals in sibling pairs who were interviewed at Wave I and who were eligible for inclusion in the Wave II, III, and IV samples. Response rates for the sibling pairs sample are quite high, especially at Wave II, only 1 year following Wave I, when 95% of the siblings in the pairs sample were re-interviewed. Even at Wave IV, almost 15 years after Wave I, response rates are over 90% for all types of sibling pairs, 93% for both MZ and DZ twin samples.
