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Comparison of academic performance of twins and singletons in adolescence : follow-up study

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Christensen, Kaare, Petersen, Inge, Skytthe, Axel, Herskind, Anne Maria, McGue, Matthew and Bingley, Paul. (2006) Comparison of academic performance of twins and singletons in adolescence : follow-up study. BMJ, Vol.333 (No.7578). ISSN 0959-535X

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Official URL: http://dx.doi.org/10.1136/bmj.38959.650903.7C

Abstract

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.

Item Type:

Journal Article

Subjects:

L Education > LB Theory and practice of education

Divisions:

Faculty of Social Sciences > Economics

Library of Congress Subject Headings (LCSH):

Birth weight, Academic achievement -- Testing, Twins -- Ability testing, Teenagers -- Ability testing

Journal or Publication Title:

BMJ

Publisher:

BMJ Group

ISSN:

0959-535X

Official Date:

29 September 2006

Dates:

Date	Event
29 September 2006	Published

Volume:

Vol.333

Number:

No.7578

Identification Number:

10.1136/bmj.38959.650903.7C

Status:

Peer Reviewed

Access rights to Published version:

Restricted or Subscription Access

Funder:

Syddansk universitet [University of Southern Denmark]

References:

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(Accepted 23 August 2006)