Search Results Use the search box below to revise your search, or start a new search. Studies (1) Variables Publications Your query returned 1 studies. Sort by: Study Relevance Title A-Z Released/Updated Time Period Most Cited in ICPSR Bib. Variable Relevance 1. National Academy of Sciences-National Research Council Twin Registry (NAS-NRC Twin Registry), 1958-2013 [RESTRICTED] (ICPSR 36234) Gatz, Margaret; Butler, David A.