How to find a wombmate: validation of an algorithm to identify twin pairs in Linked Birth/Infant Death Files.

Linked Birth/Infant Death Files available from the National Center for Health Statistics identify an infant as a twin, but do not identify twin pairs. An algorithm based on maternal, paternal, and infant characteristics has been used to identify twin pairs, but the validity of this algorithm has never been tested. The Missouri linked birth/infant death file from 1980 to 1990 identifies twin pairs by a sequence number. The authors tested the rate and accuracy with which the algorithm identified true pairs in the Missouri file and whether estimates of risk and possible risk factors calculated from pairs of twins identified by the algorithm agreed with these characteristics as calculated from known twin pairs. The algorithm identified 96% (8,273 of 8,620) of true pairs and one false pair. Despite incomplete pair identification, and even identification of a false pair, estimates from the subset identified by the algorithm generally agreed well with characteristics measured from all twin pairs. Nonetheless, incorporation of a multiple birth sequence number into Linked Birth/Infant Death Files would enhance their utility.