Risk and Capacity: Does the Mental Capacity Act Incorporate a Sliding Scale of Capacity?

The law places considerable weight on the question of whether a person has, or lacks, mental capacity. But approaches differ over whether and how capacity assessments should be sensitive to risk. Should a more stringent test be applied where risk is high? The question has generated considerable debate among bioethicists and jurists. In this paper, we review the literature and consider the standard of capacity defined in the Mental Capacity Act 2005 in England/Wales (MCA). While the MCA has been extensively discussed, the question of whether it adopts a ‘sliding scale’ for assessments of capacity has not been squarely addressed. We review the knotty legal history of the statute regarding this issue, and argue that the MCA is best understood as adopting neither a risk-ability nor a risk-evidence sliding scale. We show that the MCA nonetheless accommodates risk-sensitivity in capacity assessment in at least three different ways. The first derives the MCA’s approach to decision-specificity, the second from a risk-investment sliding scale, the third from what Law Commission once described as a ‘general authority’ for carers to act. We argue that the resulting approach steers around two objections that critics have levied against sliding scales for capacity assessment.