Normal variation and abnormality: an empirical study of the liability distributions underlying depression and delinquency

摘要: BACKGROUND: Scale scores in studies of emotional and behavioural problems often possess highly skewed distributions. The long upper tails these distributions place a small proportion the population at some distance from main body distribution. This invites an interpretation their forming abnormal group, one that may be qualitatively distinct. METHODS: Item-response models were fitted to data on parent self-rated depression delinquency four large samples children or adolescents. RESULTS: We found underlying liability show very little no evidence non-normality. CONCLUSIONS: results suggest (i) nature scale largely measurement artefacts, (ii) provide distinct process generating abnormality as compared normal variation (iii) for characterising whole distribution, including normality abnormality, selection items typical current assessments is not optimal