The study was reviewed and approved by the Washington University Human Research Protection office (IRB), and authorized by the DSS, with a waiver of informed consent, a stipulation of which was that the research data set had to have the following characteristics (in order to avoid any possibility that individual subjects could be identified after the data merge procedure): 1) a low total number of variables; 2) each variable with a limited number of values; 3) no variables in which a given value would identify a specific subject or family.
