Comparison of general practitioner records and patient self-report questionnaires for estimation of costs.

This study compared resource use data and estimated costs over a 12-month period, based on patient self-report questionnaires and general practitioner records. The level of agreement was measured by weighted kappa. Differences in total costs were plotted against mean total costs. Of 324 patients with complete GP records for the period only 85 (26.2%) had complete self-report data. The recorded number of contacts per patient was higher for patient questionnaires than GP records (17.20 vs. 12.64), and the level of agreement between the two sources was moderate (kappa(w)=0.465). The plots of differences in total costs showed a slight downward bias, suggesting that estimation of total cost from GP records is lower than patient questionnaires. The incompleteness of patient questionnaires forces reliance on GP records as the main source of information for economic evaluations.