How specific is specific impairment?

Objective: To describe the usefulness of impairment items placed at the end of each diagnostic section of a structured instrument (the Diagnostic Interview Schedule for Children Version 2.3) in an attempt to link impairment to specific diagnoses. Method: Data from 3 sites of the Methods for the Epidemiology of Child and Adolescent Mental Disorders Study were used to assess the reliability of the specific impairment measures by diagnosis, the extent to which global and specific measures of impairment impact on prevalence rates, the concordance between global and specific impairment, and the degree to which there may be a 'halo effect' among specific impairment ratings. Results: Test-retest reliability was better for parent than youth ratings. Fewer children were rated as impaired on well-validated global scales than on specific impairment ratings, suggesting that the threshold for specific ratings needs to be reevaluated. Agreement between specific and global ratings was poor. Most subjects with 2 or more diagnoses for which impairment was attributed to one diagnosis also had impairment attributed to other diagnoses for which they met symptom criteria, suggesting a halo effect in these ratings of specific impairment. Conclusions: Impairment measures are important in diagnostic assessments to distinguish those individuals whose psychopathology is of clinical significance. Specific impairment ratings used in structured instruments could be improved by including parameters of impairment that are diagnosis-specific.