Similarities and differences in 24 identical twin pairs were evaluated using the semantic differential. The subjects rated their twins as being very similar to themselves; more similar than was indicated when this rating was compared with the twin rating of themselves. Thus, the subjects appeared to project their own self-image on to their twins.
This degree of projection was positively correlated with the twin rating of how they liked being a twin, how close they felt to each other, and similarities in hobbies and interests. No positive correlation was found between the degree of projection and how frequently the twins saw each other or the twin assessment of their physical resemblance.
Forming other relationships (as measured by marriage) showed random distribution. In the twins who showed the greatest degree of projection, however, there were some problems in separating from their twins.
Paluszny M, Beit-Hallahmi B. An Assessment of Monozygotic Twin Relationships by the Semantic Differential. Arch Gen Psychiatry. 1974;31(1):110-112. doi:10.1001/archpsyc.1974.01760130084014