Incidence of anorexia nervosa
The studies which counted only hospitalized patients tended to yield low estimates of the annual incidence of anorexia nervosa expressed per 100 000 population (e.g. 0.45 in Sweden(l7)). Estimates based on case registers of psychiatric patients similarly yielded fairly low incidence rates (e.g. 0.64 in Monroe County, New York(18>). The incidence found in community-based studies was by far the highest (6.3 in The Netherlands (l1) and 8.2 in Rochester, Minnesota^.1.,)), presumably because they included the less severe cases.
Prevalence of anorexia nervosa in vulnerable populations
A high prevalence rate was found among Canadian ballet students (6.5 per cent) and modelling students (7 per cent). (12) A similar survey in an English ballet school also showed a high prevalence of 'possible' cases of anorexia nervosa (7.0 per cent). (1.3>
Surveys among schoolgirls have shown a fairly wide variation in prevalence rates, ranging from zero to 1.1 per cent. In the English studies a consistent difference in prevalence rate was found between private schools (1 per cent) and state schools (0-0.2 per cent). (1, i5) This social class distinction was not so definite in the Swedish study where the overall prevalence of 0.84 per cent of schoolgirls, up to and including 15 years of age, represents a high rate for anorexia nervosa. (1..6)
Epidemiological surveys have confirmed clinical opinion that anorexia nervosa commences most frequently in the young, especially within a few years of puberty. The peak age of onset is 18 years/1.4 The illness is less common before puberty, but in a series of patients admitted to a children's hospital the age of onset ranged from 7.75 to 14.33 years. (22>
anorexia nervosa 'is much more common in wealthier classes of society than amongst those who have to procure their bread by daily labour'. (23)
Epidemiological surveys aimed at wider populations leave the question of social class distribution somewhat equivocal. Whereas a high percentage of combined social classes 1 and 2 (Registrar General's categories) were found in clinical studies, (24) a high social class predominance was not found in studies utilizing case registers.1,' On the other hand, the schoolgirl studies mentioned above tended to confirm a high social class predominance.
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