To examine the power to test the primary hypotheses with the EGDS sample of 360 triads, we modeled several alternative values based on genetic and environmental effects in prior studies. Effect sizes for genetic effects were estimated to range from 0.10 to 0.50 based on findings of birth parents' effects on adolescent adoptees (β = 0.31 and 0.42; Ge et al. 1996; O'Connor et al. 1998). Using a 92% retention rate (current retention rates are 93% for adoptive families, 92% for birth mothers, and 91% for birth fathers), we estimated whether the EGDS sample of 360 triads (N = 331 when a 92% retention rate is assumed) would be sufficient for detecting significant genetic and environmental main effects, significant G × E interaction effects, and model fit in SEM. Power analyses suggested that a sample of 331 triads would provide power well above 0.90 for detecting genetic and environmental main effects, power of 0.50–0.98 for detecting G×E interaction effects, and power of 0.78–0.93 for model testing in SEM, suggesting that the EGDS is sufficiently powered. Further, the inclusion of 200 additional triads (currently underway) will increase our ability to detect effects that are small in magnitude.
