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Science 22 June 2007:
Vol. 316. no. 5832, p. 1717
DOI: 10.1126/science.1141493
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Brevia

Explaining the Relation Between Birth Order and Intelligence

Petter Kristensen1,2* and Tor Bjerkedal3

1 National Institute of Occupational Health, N-0033 Oslo, Norway.
2 Section for Preventive Medicine and Epidemiology, University of Oslo, N-0318 Oslo, Norway.
3 Institute of Epidemiology, Norwegian Armed Forces Medical Services, N-0015 Oslo, Norway.


Figure 1 Fig. 1. Relation between birth order and IQ score. Mean IQ scores for male conscripts, first-, second-, and thirdborn in Norway to mothers with single births only and first birth from 1967 through 1976, according to birth order and number of elder siblings who died in infancy (age < 1 year). Scores are adjusted for parental education level, maternal age at birth, sibship size, birth weight, and year of conscription. Error bars show 95% confidence intervals (CIs). Reference: birth order one. [View Larger Version of this Image (18K GIF file)]
 

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Science. ISSN 0036-8075 (print), 1095-9203 (online)