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. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript.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.</p>

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