Educational attainment of same-sex and opposite-sex dizygotic twins: An individual-level pooled study of 19 twin cohorts
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Date
2021-11Author
Silventoinen, Karri
Bogl, Leonie H.
Jelenkovic Moreno, Aline
Vuoksimaa, Eero
Latvala, Antti
Li, Weilong
Tan, Qihua
Zhang, Dongfeng
Pang, Zengchang
Ordoñana Martín, Juan Ramón
Sánchez Romera, Juan Francisco
Colodro Conde, Lucía
Willemsen, Gonneke
Bartels, Meike
van Beijsterveldt, Catharina EM
Rebato Ochoa, Esther Matilde
Corley, Robin P.
Huibregtse, Brooke M.
Hopper, John L.
Tyler, Jessica
Duncan, Glen E.
Buchwald, Dedra
Silberg, Judy L.
Maes, Hermine H.
Kandler, Christian
Cozen, Wendy
Hwang, Amie E.
Mack, Thomas M.
Nelson, Tracy L.
Whitfield, Keith E.
Medda, Emanuela
Nisticò, Lorenza
Toccaceli, Virgilia
Krueger, Robert F.
McGue, Matt
Pahlen, Shandell
Martin, Nicholas G.
Medland, Sarah E.
Montgomery, Grant W.
Heikkilä, Kauko
Derom, Catherine A.
Vlietinck, Robert F.
Loos, Ruth JF
Magnusson, Patrik KE
Pedersen, Nancy L.
Dahl Aslan, Anna K.
Hotopf, Matthew
Sumathipala, Athula
Rijsdijk, Fruhling
Siribaddana, Sisira H.
Rose, Richard J.
Sørensen, Thorkild IA
Boomsma, Dorret I.
Kaprio, Jaakko
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Hormones and Behavior 136 : (2021) // Article ID 105054
Abstract
Comparing twins from same- and opposite-sex pairs can provide information on potential sex differences in a
variety of outcomes, including socioeconomic-related outcomes such as educational attainment. It has been
suggested that this design can be applied to examine the putative role of intrauterine exposure to testosterone for
educational attainment, but the evidence is still disputed. Thus, we established an international database of twin
data from 11 countries with 88,290 individual dizygotic twins born over 100 years and tested for differences
between twins from same- and opposite-sex dizygotic pairs in educational attainment. Effect sizes with 95%
confidence intervals (CI) were estimated by linear regression models after adjusting for birth year and twin study
cohort. In contrast to the hypothesis, no difference was found in women (β = - 0.05 educational years, 95% CI
- 0.11, 0.02). However, men with a same-sex co-twin were slightly more educated than men having an oppositesex
co-twin (β = 0.14 educational years, 95% CI 0.07, 0.21). No consistent differences in effect sizes were found
between individual twin study cohorts representing Europe, the USA, and Australia or over the cohorts born
during the 20th century, during which period the sex differences in education reversed favoring women in the
latest birth cohorts. Further, no interaction was found with maternal or paternal education. Our results
contradict the hypothesis that there would be differences in the intrauterine testosterone levels between samesex
and opposite-sex female twins affecting education. Our findings in men may point to social dynamics within
same-sex twin pairs that may benefit men in their educational careers.