In this article, the authors evaluate two brief clinician-scored global assessment instruments used to measure the functioning of adult clients who have a serious mental illness: the Global Assessment of Functioning (GAF) Scale and the relatively new Kennedy Axis V (K Axis). Although both instruments are brief and easy to score, the K Axis provides a multi-dimensional evaluation, while the GAF provides a single, unidimensional picture of a client's functioning. Statistical analyses indicated that both instruments have adequate validity and reliability if the clinicians using them are sufficiently trained. Correlations between the two instruments were high where expected. Statistically significant differential functioning was found for various subgroups. The K Axis was better able to pinpoint this specific differential functioning.
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