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Birth Order and Physical Fitness in Early Adulthood: Evidence from Swedish Military Conscription Data
Stockholm University, Faculty of Social Sciences, Department of Sociology.
Department of Social Policy, London School of Economics and Political Science, UK.
2014 (English)In: Social Science and Medicine, ISSN 0277-9536, E-ISSN 1873-5347, Vol. 123, 141-148 p.Article in journal (Refereed) Published
Abstract [en]

Physical fitness at young adult ages is an important determinant of physical health, cognitive ability, and mortality. However, few studies have addressed the relationship between early life conditions and physical fitness in adulthood. An important potential factor influencing physical fitness is birth order, which prior studies associate with several early- and later-life outcomes such as height and mortality. This is the first study to analyse the association between birth order and physical fitness in late adolescence. We use military conscription data on 218,873 Swedish males born between 1965 and 1977. Physical fitness is measured by a test of maximal working capacity, a measure of cardiovascular fitness closely related to V02max. We use linear regression with sibling fixed effects, meaning a within-family comparison, to eliminate the confounding influence of unobserved factors that vary between siblings. To understand the mechanism we further analyse whether the association between birth order and physical fitness varies by sibship size, parental socioeconomic status, birth cohort or length of the birth interval. We find a strong, negative and monotonic relationship between birth order and physical fitness. For example, third-born children have a maximal working capacity approximately 0.1 (p<0.000) standard deviations lower than first-born children. The association exists both in small (3 or less children) and large families (4 or more children), in high and low socioeconomic status families, and amongst cohorts born in the 1960s and the 1970s. While in the whole population the birth order effect does not depend on the length of the birth intervals, in two-child families a longer birth interval strengthens the advantage of the first-born. Our results illustrate the importance of birth order on physical fitness, and suggest that the first-born advantage already arises in late adolescence.

Place, publisher, year, edition, pages
Elsevier, 2014. Vol. 123, 141-148 p.
Keyword [en]
Birth Order, Physical Fitness, Sibling Comparison, Fixed Effects, Military Conscription Data, Sweden, Register Data
National Category
Sociology (excluding Social Work, Social Psychology and Social Anthropology)
Research subject
Demography; Sociology
URN: urn:nbn:se:su:diva-108833DOI: 10.1016/j.socscimed.2014.11.007ISI: 000347021800017OAI: diva2:760833
EU, European Research Council, 2013-StG-336475
Available from: 2014-11-04 Created: 2014-11-04 Last updated: 2015-02-02Bibliographically approved
In thesis
1. The Long-term Impact of Birth Order on Health and Educational Attainment
Open this publication in new window or tab >>The Long-term Impact of Birth Order on Health and Educational Attainment
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This doctoral thesis examines the long-term impact of birth order on health, and educational attainment. Swedish register data is used to link individuals to their siblings, thereby allowing members of the sibling group to be compared to one another. This thesis consists of an introductory chapter summarizing empirical research on the relationship between birth order and educational attainment, intelligence, health, and personality, as well the theoretical frameworks that have been developed to explain those relationships. This introductory chapter is followed by four original empirical studies. The first two studies show that relative to first born siblings, later borns have lower physical fitness in late adolescence, and higher mortality in adulthood. The third study uses the Swedish registers to identify sibling groups that entirely consist of adopted individuals, and shows that the commonly observed negative relationship between birth order and educational attainment persists in these fully adopted sibling groups. These results suggest that birth order effects are likely explained by post-natal, social mechanisms within the family. Finally, the fourth study shows that even though later born siblings do worse than first borns in a fully adjusted statistical model, educational expansion in the 20th century has meant that later born siblings actually tend to have greater educational attainment and are more likely to attend university in comparison to older siblings within the same family.  

Place, publisher, year, edition, pages
Stockholm: Department of Sociology, Stockholm University, 2014. 115 p.
Stockholm studies in sociology, ISSN 0491-0885 ; N.S., 59
Birth Order, Health, Mortality, Educational Attainment, Sibling Comparison, Fixed Effects, Sweden, Register Data
National Category
Sociology (excluding Social Work, Social Psychology and Social Anthropology)
Research subject
urn:nbn:se:su:diva-108841 (URN)978-91-7649-051-8 (ISBN)
Public defence
2014-12-19, hörsal 3, hus B, Universitetsvägen 10 B, Stockholm, 10:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Epub ahead of print. Paper 3: Accepted. Paper 4: Manuscript.

Available from: 2014-11-27 Created: 2014-11-04 Last updated: 2014-11-21Bibliographically approved

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Barclay, Kieron
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