THE RELIABILITY OF PATIENTS JUDGMENTS OF CARE IN GENERAL-PRACTICE - HOW MANY QUESTIONS AND PATIENTS ARE NEEDED

Objectives-To estimate the number of questions and patients that are n eeded to achieve reliable measurements of patients' judgements of are in general practice. Design-Sensitivity study, using generalisability theory and real data from surveys of patients. Subjects-739 patients w ith chronic illness from 23 general practitioners in The Netherlands. Main measures-The reliability coefficients of scores per patient and s cores per general practitioner for patients' judgements of nine dimens ions of care in general practice. Results-For most dimensions the reli ability per patient was 0.80 or higher if three questions were used, b ut for the evaluation of the ''organisation appointments'' and ''premi ses'' five questions had to be used. To reach a reliability coefficien t of 0.80 per general practitioner three questions and 90 patients, or five questions and 60 patients, were needed for most dimensions. Even more patients or questions were needed for the dimensions ''availabil ity for emergencies'', premises, and ''continuity''. A reliability of 0.70 per general practitioner could be achieved if three questions and 60 patients were used, except for availability for emergencies and pr emises, for which more patients or questions were required. Conclusion s-Surveys of patients can only provide reliable information if the sam ples of questions and patients are large enough. It is important to di stinguish between the reliability of scores per patient and the reliab ility per care provider, as well as between different dimensions of ca re. The reliability per patient is good for most dimensions if three q uestions are used, but a good reliability per care provider requires m ore questions or patients.