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Later birth order is associated with minimally lower IQ (NEJM JW Psychiatry Sep 2007 and Science 2007; 316:1717), but less is known about relationships of birth placement to personality factors. These investigators conducted analyses of 3156 within-family sibships and 17,030 between-family cases in the U.S., the U.K., and Germany.
Self-reported data from questionnaires covered the “Big Five” personality areas (extraversion, emotional stability, agreeableness, conscientiousness, and openness). Analyses controlled for sibship age; sibships involving more than four siblings were excluded because they were uncommon. No significant differences occurred by sibling order in any area except for a subtest of openness called “Intellect,” which assesse…