The remaining twin pairs (529 total pairs; 218 male and 311 female) were randomly assigned to the unscreened sample. These twin families were recruited without prior screening, other than for physical or intellectual disability that precluded completing the assessment or for living within a day's drive of the University. The recruitment of the unscreened ES sample was designed to mirror MTFS twin recruitment. The proportion of the total sample randomized to the unscreened and screened samples was set to ensure that all pairs that screened above threshold and were willing to participate could be accommodated in the 500 recruitment slots available, while inclusion of an unscreened sample facilitated comparison with the unselected MTFS twins.
