Differential environmental factors in anorexia nervosa: a sibling pair study.

OBJECTIVES Previous studies have explored differences in psychosocial and familial factors between women who develop anorexia nervosa and those who do not. However, these studies have generally used between-group comparisons. This study looks at the environmental factors which may be antecedents of anorexia nervosa looking at sister pairs where one had anorexia nervosa and the other did not. DESIGN A paired design was used to compare anorexic women with an unaffected sister on a number of background variables, including sibling interaction, parental care, peer group characteristics and other events unique to the individual. METHODS The Sibling Inventory of Differential Experience (SIDE) was used to determine non-shared environment. Out of an initial sample of 148 women with past or current anorexia nervosa, 28 were identified who had sisters with no reported history of eating disorders and who also consented to complete the questionnaire. RESULTS Anorexic sisters perceived more maternal control and reported more antagonism towards and jealousy of their sisters than did unaffected sisters. In addition, anorexic women reported having had fewer friends and boyfriends than their sisters. CONCLUSIONS These results confirm the perceived differences in background environment between women with and women without anorexia nervosa. These issues are discussed in relation to behavioural genetics, family dynamics and psychosexual development.