Valuing the benefits of publicly-provided health care: does 'ability to pay' preclude the use of 'willingness to pay'?

The case against the use of willingness to pay (WTP) methods to value the benefits of publicly-provided health care is often made on the basis that WTP is associated with ability to pay. In this paper, it is demonstrated that this argument is not so straightforward, depending on two criteria: (a) the association of people's preferences with ability to pay and (b) the disparities of WTP for given options within categories of ability to pay. A method of dealing with ability to pay, based on these criteria, is proposed and illustrated through the use of data from a case study.