Reliability of the Aberrant Behavior Checklist and the effect of variations in instructions.

Interrater and test-retest reliabilities of the Aberrant Behavior Checklist were compared on the basis of type of instructions to raters. Three nurses in each of three residential units twice rated 28 mentally retarded residents, using one type of rating system, and the ratings were repeated 4 weeks later. The frequency-based instructions resulted in both higher interrater and test-retest reliability coefficients than did the other instructional types. Frequency-based ratings were performed again in another residential unit, but the higher reliabilities were not replicated. Interrater and test-retest reliability correlations varied markedly both across subscales and raters but were comparable to levels derived with other symptom checklists. We concluded that rater characteristics (e.g., motivation) are more powerful variables than are scoring systems.