Bias measuring bias.

The British National Health Service and other publicly funded health systems operate on the principle that health care should be provided solely on the basis of need. Yet the literature abounds with reports of bias in health care use. In order to defend such a charge, two conditions must be met. The first condition is that treatment decisions must be shown to be unfair in that they are not made solely on the basis of need. This paper demonstrates the importance of considering the fair distribution of health care from two, related, perspectives. The first is that people with equal needs should be treated the same (equal use for equal need). This is referred to as the achievement of horizontal equity. The alternative perspective is that people with greater needs should have more treatment than those with lesser needs (unequal use for unequal need). This is referred to as the achievement of vertical equity. Although these perspectives are logically linked, demonstration of equal use for equal need does not necessarily indicate unequal use for unequal need. This is because it cannot be assumed that equal use occurs at every level of need. The second condition that must be met is that clinical judgement must be shown to be influenced by prejudicial notions about patients. Such research is fraught with methodological difficulties, and the charge of biased clinical decision-making is usually made as a result of a process of exclusion. Methods that could be used to examine the extent to which inequalities in health care use are due to bias are described.