An experiment of mailing physician surveys on two different issues in joint or separate mail

High response rates from physicians play an important role in obtaining valid data on practice patterns. We wanted to know whether two questionnaires (one on hernia surgery and one on perioperative pain management) should better be sent out in one letter or two separate letters. We randomized 2,393 surgeons who received the two questionnaires either in one letter or by separate mail, in two letters, at a time interval of 4 weeks. The response rate for the separate mailout was not significantly higher when compared to the joint mailout. The differences were 3.3% (95%-CI -0,4% to 7.1%) and 2.2% (95%-CI - 1,4% to 5.9%) for the two surveys. Due mainly to higher postage costs, the costs per response were doubled in the separate mailout group (5.85 Euro versus 2.93 Euro). Sending out two surveys separately seems to have only little effect on the response rates. (C) 2002 Elsevier Science Inc. All rights reserved.