Comparison of alternative methods of collection of service use data for the economic evaluation of health care interventions

Economic evaluation of health care interventions usually requires the collection of service use data to estimate the total cost of participants in an evaluation. There are a number of methods available to measure the quantity of services used but little is known about the relative accuracy of alternative methods. In a multicentre randomised controlled trial of interventions for the treatment of adults with recurrent episodes of deliberate self-harm (the POPMACT trial), health service data were collected by patient self-report after six and twelve months and also from GP records by independent investigators. Agreement for overall costs was relatively high. However, this hides substantial variation in agreement between the two sources of information for different services. The results suggest that GP records provide more accurate data on the use of general practice-based contacts than patient report, but less reliable information on contacts with other health services. Thus reliance on GP records for data on hospital services and other community health services based outside of general practice surgeries is not recommended. Future research should explore the level of agreement between patient report and other providing sector records, such as hospital records.