ABSTRACT
The subject cohorts were chosen as they presented themselves to us, and we had sufficient time to add them to our sample. It was on the basis of chance that each cohort was added to the sample, and sample size of the original set of five families was dictated by time considerations. We added three sets of triplets, that are not part of the basic sample. Triplets A were followed through two years; Triplets B were seen only at three months; Triplets C were seen at 9 years of age. These data are presented in some of the chapters for comparative purposes.
