Evaluating prognostic factors: implications for measurement of health care outcome.

Measurement ofhealth care outcomes has become the contemporary philosophers' stone for public health researchers, managers, and politicians alike. Each group recognises that the rational use of scarce resources depends on measuring the effectiveness of different procedures and programmes of care. 1 This point was clearly made by Cochrane in 19722 and there has since been increasing interest in developing indicators of health care outcome.3 Donabedian defined (health care) outcome as "those changes either favourable or adverse in the actual or potential health status of persons, groups or communities that can be attributed to prior or concurrent care".' Attributing changes in health status to prior or concurrent care is no simple matter and there is continuing uncertainty concerning how this can and cannot be done.5