The General Practice Assessment Survey (GPAS): tests of data quality and measurement properties.

The aim of this study was to describe the psychometric properties of the General Practice Assessment Survey (GPAS) and its acceptability to patients in the UK. GPAS comprises seven multiple item scales and two single item scales addressing nine key areas of primary care activity (access, technical care, communication, inter-personal care, trust, knowledge of patient, nursing care, receptionists and continuity of care). A further four single items relate to patients' perceptions of the GP's role in referral and co-ordination of care, their willingness to recommend their GP and their overall satisfaction with care received. Two hundred consecutive patients attending routine consulting sessions at 55 inner London practices were invited to complete the GPAS questionnaire. The acceptability, reliability and validity of GPAS was assessed using standard psychometric techniques. Out of 11 000 patients, 7247 (66%) completed a questionnaire in a GP surgery. Fifty-five out of a separate sample of 77 patients attending one practice completed a second questionnaire mailed to them 1 week following their attendance. GPAS was acceptable to patients as evidenced by low proportions of missing data for all items, and a full range of possible scores for all but one of the nine scales. Reliability of the instrument was good. Multiple item scales had excellent internal consistency, high item-total correlations, and test-retest reliability. Scaling assumptions were confirmed, with six of the seven scales achieving 100% scaling success (convergent and discriminant validity). Construct validity was evident, although this requires further evaluation against external measures. GPAS is a useful instrument for assessing several important dimensions of primary care. It is acceptable, reliable and valid, and has the potential for versatility in mode of administration. It will be a useful instrument for practices, primary care groups and primary care researchers evaluating key areas of primary care activity. Further work is required to evaluate its performance in non-inner-city settings and to evaluate further its validity against external criteria.