Twin and adoption studies suggest that differences in shared environments e.g., overall family, warmth, social class, and other features of the family environment that siblings share) account for approximately what percentage of the variance of trait scores?

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Twin and adoption studies have shown that shared environments (e.g., overall family warmth, social class, and other features of the family environment that siblings share) typically account for a very small percentage of the variance in trait scores, often estimated at 0%-5%. This suggests that genetic factors and unique environmental experiences (those not shared between siblings) play a larger role in individual differences in traits.

Twin and Adoption Studies Suggest That Differences in Shared Environments