Background: Previous studies have found the Mini-mental State Examination (MMSE) predictive of capacity to consent to power of attorney and to enter into residential care. We aimed to assess the utility of the MMSE in predicting capacity to consent to research in elderly U.K. care home residents, to determine the optimal cut-point score, and to ascertain which items of the MMSE most predicted capacity.
Methods: Care home residents (n = 227) who had been recruited into a randomized controlled trial and assessed for capacity to consent were subsequently administered the MMSE and a measure of depression. A receiver operator characteristic (ROC) curve was generated and the maximal MMSE cut-point that best predicted capacity status determined. Multiple regression analyses were conducted to assess the effect of other variables on capacity status.
Results: The area under the ROC curve was 0.86 (p < 0.001, 95% CI 0.80–0.91). The optimal cut-point was 13/14, which provided a positive predictive value of 0.84 (0.79–0.89) and negative predictive value of 0.69 (0.62–0.75). The odds ratio of a MMSE score ≥14 predicting having capacity was 11.95 (6.03–23.94). Depression reduced the odds of having capacity (OR 0.32, 0.17–0.62, p = 0.001). All individual items of the MMSE apart from following a written command (“close your eyes”) had odds ratios significantly associated with capacity status. The item most associated with capacity status was being able to verbally repeat a sentence (“no ifs, ands, or buts”) correctly (OR 5.6, 95% CI 3.0–10.5).
Conclusions: The MMSE is predictive of capacity to consent to research and may have a role in guiding researchers in this domain. It should not, however, be used in lieu of a formal capacity assessment as even the optimal cut-point of 13/14 mislabeled 24% of capable subjects as lacking capacity, and 21% of incapable subjects as having capacity.