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Table 1 Interpretation of twin correlations

From: A longitudinal twin study of the association between childhood autistic traits and psychotic experiences in adolescence

Component Cross-twin correlation Cross-trait cross-twin correlation
Additive genetic (A) MZ correlation is higher than the DZ correlation MZ correlation is higher than the DZ correlation
Shared environmental (C) DZ correlation is greater than half the MZ correlation DZ correlation is greater than half the MZ correlation
Nonshared environmental (E) MZ correlation is lower than 1 MZ correlation is lower than the phenotypic correlation
  1. Cross-twin correlation: correlation of one twin’s score on a trait with their co-twin’s score on the same trait; cross-trait cross-twin correlation: correlation of one twin’s score on a trait with their co-twin’s score on another
  2. MZ monozygotic twins, DZ dizygotic twins