ABSTRACT
The East Flanders Prospective Twin Survey (EFPTS) was established on July 15, 1964, in the Province of East Flanders in Belgium. The province covers 10% of Belgian territory, and is inhabited by approximately 13% (1 336 000 inhabitants) of the Belgian population; the great majority are Caucasian and tend to remain in the same residence for years, if not decades. As such, they are easily traceable, even after 40 years.
