Individual differences are also thought to be important in the development of eating disorders, though the research is not as strong in this area. There appears to be a genetic component to anorexia nervosa and bulimia nervosa, as seen in twin studies and studies of the relatives of anorexics and bulimics. The genetic disposition may manifest itself in personality, as adolescents and women with eating disorders are often characterized by obsessional tendencies, rigidity, and poor adaptability (Wilson, Heffernan, & Black, 1996). Strober (1980) investigated the personalities of adolescent anorexics. Although the study is not longitudinal and relies on self-report, it does show that certain personality variables are unique to anorexic adolescents. Participants were 22 females between the ages of 12.8 and 16.5 who were admitted to hospital treatment after an initial diagnosis of anorexia. They were compared to normal-weight adolescents in the same hospital who had been diagnosed with either affective disorder or personality or conduct disturbances. Anorexics were found to be obsessional, introverted, lacking in autonomy, self-abasing, and rigid. Again, these findings should be viewed with caution due to the methodology of the study; it is not clear whether these personality variables are present before the onset of anorexia or they are a result of it.