Reliability of psychiatric and psychological diagnoses of mental retardation severity: judgments under naturally occurring conditions.

The reliability of diagnoses of mental retardation severity was examined through the comparison of psychiatric and psychological case reports found in client records. For a sample of 126 dually diagnosed clients, overall chance-corrected agreement was .47, ranging from .38 (for diagnoses of moderate mental retardation) to .55 (for diagnoses of borderline mental retardation). Results showed that the analysis of naturally occurring variation in diagnostic practices (including variability in professional judgment and assessment methods) may offer a more realistic appraisal of the reliability of diagnostic decisions in professional practice situations than do studies in which important sources of diagnostic error are controlled.