The National Merit Twin Study

The National Merit Twin Study includes extensive questionnaire data from 839 sets of adolescent twins and a parent. The twins were identified among the roughly 600,000 US high school juniors who took the National Merit Scholarship Qualifying Test in 1962. They were diagnosed as identical (N=509 pairs) or same-sex fraternal (N=330 pairs) by a brief mail questionnaire, and later completed a 1082-item questionnaire covering a variety of behaviors, attitudes, personality, life experiences, health, vocational preferences, etc., plus the 480-item California Psychological Inventory. The twins' scores on the National Merit Scholarship Qualifying Test and its 5 subscales are also included. The 285-item questionnaire filled out by the parent was mainly focused on the life histories and experiences of the twins. The study is described in J. C. Loehlin and R. C. Nichols, Heredity, Environment, and Personality, University of Texas Press, 1976. Altogether, along with a number of derived variables, the SPSS files contain 1610 items for each twin plus 313 for the parent, or 3533 variables on 839 cases. The files are: nmvars.doc A list of the variables in the study twinq.pdf The questionnaire filled out by the twins parq.pdf The questionnaire filled out by a parent nmgen.sav All study variables, except for some item-level data obitem.sav Item-level data on the Objecti ve Behavior Inventory acitem.sav Item-level data on the Adjective Check List vpitem.sav Item-level data on the Vocational Preference Inventory cpitem.sav Item-level data on the California Psychological Inventory Items for the first three of the last four files are included in the twin questionnaire booklet. For the CPI items, see the California Psychological Inventory (Consulting Psychologists Press, Palo Alto, 1957). Variable numbering and scoring are specified in nmvars.doc.