Dizygotic twin correlations for educational attainment are consistently higher than non-twin sibling correlations across countries, suggesting twin-specific shared environments are a general phenomenon¶

Claim · All claims
Evidence · 1 study · associational r2 · q2
Currency · newest study 2023 · not yet checked against its sources · not reviewed by a person

Subclaims¶

q2 i? A survey of prior studies found rDZ exceeded rSIB in every country comparison compiled by the authors, indicating twin-specific environments may generalise beyond the TwinLife sample. → Wolfram 2023

Evidence¶

Wolfram 2023¶

Wolfram, T. & Morris, D. (2023). Conventional twin studies overestimate the environmental differences between families relevant to educational attainment. npj Science of Learning 8, 24. https://doi.org/10.1038/s41539-023-00173-y

q2 · i? · associational · r2

Comparative re-analysis presented in Table 2, compiling sibling and DZ twin correlations for educational attainment from registers and twin studies in Finland, Germany, Norway, Sweden, the UK, and the USA. DZ twin correlations were "invariably higher" than sibling correlations.

"when we compared sibling correlations for EA from a recent international study 8 with DZ twin correlations from studies in the same countries with similar birth cohorts, the DZ twin correlations were invariably higher"

Discussion¶

Related Claims¶

• A Classical Twin Design model of educational attainment in the TwinLife sample estimates shared environmental influence at 43% and additive genetic influence at 34% — related
• Twin-specific shared environments account for a substantial portion of CTD shared-environment estimates for educational attainment and cannot be interpreted as between-family environmental differences — related
• The best-fitting NTFD model estimates heritability of educational attainment at 51% and total shared environmental influence at 26%, disaggregated into twin-specific (16%) and sibling-shared (10%) components — related