For research purposes, we use a form of zygosity determination called “self-report.” This determination uses the responses that you and your twin provided to two questions on the recruitment survey that you completed when you joined the Registry. These questions are “When you and your twin were children, were you as alike as two peas in a pod or of ordinary family resemblance?” and “How often did parents, relative, teachers, and strangers have trouble telling you and your twin apart?”
Based on the answers that you and your twin provided, and comparing your answers with those of other twins in the Registry, we have developed a method that can predict zygosity with about 96% accuracy. We use this “self-report” zygosity to generate the statistics for our website, and to recruit twins for our studies. It is extremely helpful for research and statistical purposes, since this level of accuracy is enough to reflect group trends and tendencies.