A comparison of response rate and time according to the survey methods used: a randomized controlled trial.

The purpose of this study was to evaluate the effects of recorded and standard deliveries, and stamped and franked return envelops in a postal survey of Korean-Vietnam veterans. Nine hundred veterans were randomly divided into four subgroups. A randomized controlled trial was conducted for two mailing strategies. The 52 study subjects to whom mail was undeliverable and 36 additional study subjects found not to be residing at the listed addresses were excluded from the study. The 699 (86%) surveys were returned within 39 business days after the first mailing. The response rate for the recorded delivery (88%) was significantly higher than that of the standard delivery (82%)(p = 0.03), and the response rate of the stamped return envelops (88%) was higher than that of the franked return envelops (85%)(p = 0.27). The replies for the recorded and standard deliveries arrived an average of 10.2 and 9.9 business days, respectively, after the first mailing (p = 0.60). The average times of the responses for the stamped and franked return envelops were 9.8 and 10.4 business days, respectively (p = 0.25). Recorded deliveries significantly increased the response rate compared to standard deliveries, and stamped return envelops slightly increased the response rate a little compared to franked return envelops. The timing of response of recorded deliveries was similar to that of standard deliveries but the volume of response of recorded deliveries was higher than that of standard deliveries.