The effect of two mailing strategies on the response to a survey of physicians

In 1989, the authors tested the effectiveness of two response-enhancing techniques, a postage stamped or franked return envelope and a prenotification letter, in a survey of pregnancy among 10,047 resident physicians in the United States. The techniques were randomly assigned using a factorial design. No significant interactions were observed between the techniques. After two mailings, those who received a stamped return envelope had a response of 71.2%, compared with 68.2% for those who received a franked return envelope (95% confidence interval 1.3-4.9%). Men who received the stamped envelope had a 5.9% greater response than those who received the franked envelope (p less than 0.001), but the type of postage did not influence response among women (p = 0.84); this interaction was statistically significant (p = 0.006). Physicians who received a prenotification letter had a response of 69.0%, compared with 70.5% for those who did not receive the letter (95% confidence interval -3.3 to 0.2%). The authors conclude that seemingly minor changes in survey design could have saved from 12% to 19% of the total cost of the study.