TY - JOUR
T1 - Comparison of academic performance of twins and singletons in adolescence
T2 - Follow-up study
AU - Christensen, Kaare
AU - Petersen, Inge
AU - Skytthe, Axel
AU - Herskind, Anne Maria
AU - McGue, Matt
AU - Bingley, Paul
PY - 2006/11/25
Y1 - 2006/11/25
N2 - Objectives: To determine whether twins in recent cohorts show similar academic performance in adolescence to singletons and to test the effect of birth weight on academic performance in twins and singletons. Design: Follow-up study. Setting: Denmark. Participants All twins (n = 3411) and a 5% random sample of singletons (n = 7796) born in Denmark during 1986-8. Main outcome measures: Test scores in ninth grade (age 15 or 16), birth weight, gestational age at birth, parents' age, and parents' education. Results: Ninth grade test scores were normally distributed, with almost identical mean and standard deviations for twins and singletons (8.02 v 8.02 and 1.05 v 1.06) despite the twins weighing on average 908 g (95% confidence interval 886 to 930 g) less than the singletons at birth. Controlling for birth weight, gestational age at birth, age at test, and parents' age and education confirmed the similarity of test scores for twins and singletons (difference 0.04, 95% confidence interval - 0.03 to 0.10). A significant, positive association between test score and birth weight was observed in both twins and singletons, but the size of the effect was small: 0.06-0.12 standard deviations for every kilogram increase in birth weight. Conclusions: Although older cohorts of twins have been found to have lower mean IQ scores than singletons, twins in recent Danish cohorts show similar academic performance in adolescence to that of singletons. Birth weight has a minimal effect on academic performance in recent cohorts; for twins this effect is best judged relative to what is a normal birth weight for twins and not for singletons.
AB - Objectives: To determine whether twins in recent cohorts show similar academic performance in adolescence to singletons and to test the effect of birth weight on academic performance in twins and singletons. Design: Follow-up study. Setting: Denmark. Participants All twins (n = 3411) and a 5% random sample of singletons (n = 7796) born in Denmark during 1986-8. Main outcome measures: Test scores in ninth grade (age 15 or 16), birth weight, gestational age at birth, parents' age, and parents' education. Results: Ninth grade test scores were normally distributed, with almost identical mean and standard deviations for twins and singletons (8.02 v 8.02 and 1.05 v 1.06) despite the twins weighing on average 908 g (95% confidence interval 886 to 930 g) less than the singletons at birth. Controlling for birth weight, gestational age at birth, age at test, and parents' age and education confirmed the similarity of test scores for twins and singletons (difference 0.04, 95% confidence interval - 0.03 to 0.10). A significant, positive association between test score and birth weight was observed in both twins and singletons, but the size of the effect was small: 0.06-0.12 standard deviations for every kilogram increase in birth weight. Conclusions: Although older cohorts of twins have been found to have lower mean IQ scores than singletons, twins in recent Danish cohorts show similar academic performance in adolescence to that of singletons. Birth weight has a minimal effect on academic performance in recent cohorts; for twins this effect is best judged relative to what is a normal birth weight for twins and not for singletons.
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U2 - 10.1136/bmj.38959.650903.7C
DO - 10.1136/bmj.38959.650903.7C
M3 - Article
C2 - 17012267
AN - SCOPUS:33845248239
SN - 0959-8146
VL - 333
SP - 1095
EP - 1097
JO - British Medical Journal
JF - British Medical Journal
IS - 7578
ER -