Actual ages of assessment were near the target ages. Pooling across cohorts in the full sample the mean (SD) ages at assessment were 11.78 (0.43), 14.90 (0.54), 17.84 (0.67), 21.09 (0.81), 24.94 (0.90). Among twins eligible for follow-up assessment, rate of participation was 93.0% at age 14, 87.3% at age 17, 89.4% at age 20, 91.0% at age 24 and 93.6% at age 29.
