When to assess mental capacity

The first principle of the Mental Capacity Act 2005 (MCA) is that capacity should be presumed. However, decision-making difficulties are common both in patients with psychiatric disorders (Bellhouse et al, 2003; Cairns et al, 2005a; Owen et al, 2008) and in general medical settings (Raymont et al, 2004). When is it legitimate to question mental capacity and make an assessment? In practice, mental capacity is called into question in three main circumstances:

The presumption of capacity places the onus on the agency making the assessment to demonstrate its absence, and the MCA and its Code of Practice (Department for Constitutional Affairs, 2007) are explicit in stating that mental capacity is not to be doubted simply on the basis of an individual's appearance or diagnosis. The point of this principle is clear, and represents the hard-fought battles of groups speaking for people with disabilities to ensure that vulnerable and stigmatised groups have a voice in decision-making. The burden of proof for assessing that someone is lacking capacity is on the ‘balance of probabilities’.

The MCA also states (in its third principle) that capacity should not be called into question simply on the basis that a decision appears to be unwise: people are at liberty to make unwise or eccentric decisions.