Measuring capacity to complete an advance directive

Abstract

Objective: To validate reference standards for the assessment of capacity to complete an advance directive and to develop and test three simple screening instruments.

Methods: We administered five measures of capacity to 96 older subjects from nursing homes, retirement homes, and homes for the aged. The measures included two reference standard evaluations: an assessment by a specially trained nurse in collaboration with a multidisciplinary team (Competency Clinic assessment) and geriatrician assessment using a decisional aid. Three screening instruments were also included: a Generic Instrument designed for any advance directive, a Specific Instrument designed for the "Let Me Decide" advance directive, and the Standardized Mini-Mental Status Examination (SMMSE). The screening instruments and the geriatrician's assessment were administered twice to half of the respondents to determine interrater agreement.

Results: The chance-corrected agreement for the assessment by two geriatricians was 0.78, and for agreement between the geriatricians and Competency Clinic assessments it was 0.82. Agreement for the Generic and Specific screening instrument assessments by two observers was 0.77 and 0.90, respectively. The areas under the Receiver Operating Characteristic curve relating the results of the three screening instruments to the Competency Clinic assessment were 0.82 for the Generic Instrument, 0.90 for the Specific Instrument, and 0.94 for the SMMSE; chance is an unlikely explanation for the difference between these three values (P < or = .01).

Conclusions: Using rigorous methods, health workers can make reproducible and valid assessments of capacity to complete an advance directive. The SMMSE accurately differentiates people who can learn about and ultimately complete advance directives from those who cannot.