Subjective outcome measurement--a primer.

There is a growing recognition within both the practice and research communities in pharmacy that serious attention must be given to the systematic study of the outcomes of pharmacy services, especially those outcomes that are focused on the patient. Research has tended to focus too strongly on the measurement of structure and process, with the unspoken assumption that if these are of good quality, the outcome will automatically be similar. However, the literature on outcome measurement instruments is vast and practitioners moving into this area for the first time may find themselves lost in a morass of conflicting definitions and different methods of measurement. This review considers the outcome measures or 'measurement instruments' that are used to assess subjective health status. Two commonly used taxonomies are described that concern the conceptual content (functional status, general health perceptions, quality of life and health-related quality of life) and the breadth of coverage of the instruments (generic, disease specific, domain or dimensions specific and patient-centred instruments). Specific attention is paid to the newest of these groups, the patient-centred instruments, which are very different in style and content to the other three and reflect a change in direction in instrument development, to address limitations of commonly used 'fixed' outcome instruments. Detail is given on what makes a quality instrument in particular circumstances (validity, reliability, sensitivity to change, multidimensional construct, practicality and applicability), to help pharmacists develop the necessary skills to select appropriate instruments in the burgeoning field of outcomes measurement.