Social Comparison Orientation in Monozygotic and Dizygotic Twins

International audienceTwin research has offered evidence that monozygotic (MZ) twins are more socially close than dizygotic(DZ) twins, but has not paid much attention to the way twins compare themselves with their co-twin. Thefew studies in this area suggest that ‘horizontal comparisons’ (social comparison motivated by solidarityor communion with others) matter more for MZ twins than for DZ twins, at least when the co-twin is thesocial comparison standard. Consistent with this view, we predicted higher interest in MZ twins relative toDZ twins to select their co-twin rather than other people in general as the social comparison standard. TheSocial Comparison Orientation (SCO) scale, which measures the inclination to compare with others in ahorizontal rather than vertical mode (comparing either upward or downward), was administered in 90 MZpairs and 57 same-sex DZ pairs (63% female; average age 18.06 years) from the Netherlands Twin Register.MZ twin pairs showed significantly higher SCO scores than DZ twin pairs (with a large effect size) on theco-twin SCO, whereas the two groups did not differ from each other on the general SCO excluding theco-twin as social comparison standard. In MZ twin pairs, anxiety was associated with social comparisonwith others in general, not with their co-twin. For both scales, twin resemblance was explained by additivegenetic variance. The present findings provide direct evidence that horizontal comparisons with the co-twinare of particular importance for MZ twins