A comparison of medical records and patient questionnaires as sources for the estimation of costs within research studies and the implications for economic evaluation.

BACKGROUND: Data on health care utilization may be collected using a variety of mechanisms within research studies, each of which may have implications for cost and cost effectiveness. OBJECTIVE: The aim of this observational study is to compare data collected from medical records searches and self-report questionnaires for the cost analysis of a cardiac secondary prevention intervention. METHODS: Secondary data analysis of the Secondary Prevention of Heart Disease in General Practice (SPHERE) randomized controlled trial (RCT). Resource use data for a range of health care services were collected by research nurse searches of medical records and self-report questionnaires and costs of care estimated for each data collection mechanism. A series of statistical analyses were conducted to compare the mean costs for medical records data versus questionnaire data and to conduct incremental analyses for the intervention and control arms in the trial. RESULTS: Data were available to estimate costs for 95% of patients in the intervention and 96% of patients in the control using the medical records data compared to 65% and 66%, respectively, using the questionnaire data. The incremental analysis revealed a statistically significant difference in mean cost of -€796 (95% CI: -1447, -144; P-value: 0.017) for the intervention relative to the control. This compared to no significant difference in mean cost (95% CI: -1446, 860; P-value: 0.619) for the questionnaire analysis. CONCLUSIONS: Our findings illustrate the importance of the choice of health care utilization data collection mechanism for the conduct of economic evaluation alongside randomized trials in primary care. This choice will have implications for the costing methodology employed and potentially, for the cost and cost effectiveness outcomes generated.