Hopes and Cautions for Instrument-Based Evaluation of Consent Capacity: Results of a Construct Validity Study of Three Instruments.

Abstract

Does instrument based evaluation of consent capacity increase the precision and validity of competency assessment or does ostensible precision provide a false sense of confidence without in fact improving validity? In this paper we critically examine the evidence for construct validity of three instruments for measuring four functional abilities important in consent capacity: understanding, appreciation, reasoning, and expressing a choice. Instrument based assessment of these abilities is compared through investigation of a multi-trait multi-method matrix in 88 older adults with mild to moderate dementia. Results find variable support for validity. There appears to be strong evidence for good hetero-method validity for the measurement of understanding, mixed evidence for validity in the measurement of reasoning, and strong evidence for poor hetero-method validity for the concepts of appreciation and expressing a choice, although the latter is likely due to extreme range restrictions. The development of empirically based tools for use in capacity evaluation should ultimately enhance the reliability and validity of assessment, yet clearly more research is needed to define and measure the constructs of decisional capacity. We would also emphasize that instrument based assessment of capacity is only one part of a comprehensive evaluation of competency which includes consideration of diagnosis, psychiatric and/or cognitive symptomatology, risk involved in the situation, and individual and cultural differences.