OBJECTIVE: To evaluate the effects of postal feedback with clinically relevant data on general practitioners' prescribing compared with feedback with aggregate data on prescribing patterns of asthma drugs.

METHODS: The study was a randomised, controlled trial. The general practitioners (GPs) in the County of Funen, Denmark (292 GPs representing 178 practices) were randomised to one of three groups receiving different forms of prescriber feedback. The first group received detailed and clinically relevant data on asthma drug prescribing patterns and a guideline statement. These data included tables with counts of asthma patients following classification of each individual's consumption of inhaled beta2-agonists and use of inhaled steroids. The second group received aggregate data on asthma drug prescribing patterns and a guideline statement, and the third group received feedback on an unrelated subject and served as control for the other groups. Each GP received prescriber feedback three times within a 6-month period. The last two letters with prescriber feedback had updated information with the purpose of showing changes in prescribing patterns. Effects were followed for a period of 1 year. The main outcome measures were change in fraction of asthmatics treated with inhaled steroids and incidence rate of treatment with inhaled steroids.

RESULTS: The three groups had similar baseline characteristics. None of the two types of feedback on prescribing of asthma drugs had a statistically significant impact on GPs' prescribing patterns.

CONCLUSION: Mailed prescriber feedback of detailed and clinically relevant data with a guideline statement, without revealing patient identities, has little or no impact on prescribing patterns.