Objective: To evaluate empirically the implications of choosing different thresholds to classify conduct disorder and attention-deficit hyperactivity disorder for estimating prevalence, test-retest reliability of measurement, and informant (parent/teacher) agreement and for evaluating comorbidity and associated features of disorder.
Method: Data for the study came from problem checklist assessments done by parents and teachers of children aged 6 to 16 years (N = 1,229) selected with known probability from a general population sample and from structured interviews obtained in a stratified, random subsample (n = 251).
Results: Estimates varied widely depending on the rationale used to set thresholds. Percent prevalence went from 0.1 to 39.2; kappa estimates of test-retest reliability went from .19 to .82. Parent-teacher agreement based on kappa went from .0 to .38. Relative odds between disorder and associated features varied twofold.
Conclusion: Use of different rationales to set thresholds for classifying childhood psychiatric disorder in the general population has profound implications for what we learn about the epidemiology of childhood disorder.