As of 2013, it is one of the largest national adult twin samples in the United States.
[2] Though it was originally formed to study the effects of military service on health, it has since been widely used to study the role of genetics in many specific mental and physical illnesses.
[3] The Vietnam Era Twin Registry was constructed by the United States Department of Veterans Affairs (VA) from military records in the 1980s.
[5] Potential twins were identified using an algorithm which aimed to identify pairs of individuals with the same last name, different first names, and similar Social Security Numbers, among other characteristics; twin status was then confirmed by examining military records.
[6] The registry was officially created in 1987[7] and was opened to non-VA investigators in 1988.