Background. Theory and evidence strongly suggest that perfectionism may be a risk factor for eating disorders. The purpose of the current study was to investigate a model that would explain the relationship between the cognitive diagnostic criterion for both anorexia nervosa and bulimia nervosa, namely undue influence of body weight or shape on self-evaluation, and dimensions of perfectionism. The model of particular interest was the common cause model, which hypothesizes that the phenotypes are caused by the same underlying genetic and environmental risk factors.

Method. Female twins (n=1002) from the Australian Twin Registry (ATR), aged 28 to 39 years, were interviewed using the Eating Disorder Examination (EDE). In addition, questions relating to the Equal Environment Assumption (EEA) and the Frost Multidimensional Perfectionism Scale, namely concern over mistakes (CM), personal standards (PS) and doubts about actions (DA), were assessed.

Results. There was no evidence of violation of the EEA for any of the four phenotypes. Univariate models showed all phenotypes to be influenced by both genetic and non-shared environmental action, where genetic estimates ranged from 25% to 39% of the variance. Multivariate analyses suggested the best explanation of covariation among the phenotypes was an independent pathways, rather than a common pathways, model.

Conclusions. Undue influence of body weight or shape on self-evaluation shared about 10% of its sources of genetic and environmental variance with perfectionism, thus suggesting that a common cause model does not represent the best explanation of the relationship between perfectionism and this cognitive diagnostic criterion for eating disorders.