Effect of stamped reply envelopes and timing of newsletter delivery on response rates of mail survey: a randomised controlled trial in a prospective cohort study

OBJECTIVE: To examine the effects of stamped reply envelope and the timing of newsletter distribution. DESIGN: A randomised controlled trial in a prospective cohort study with a 2×2 factorial design of two interventions. SETTING: The Japan Nurses’ Health Study (JNHS), a prospective cohort study for women's health. PARTICIPANTS: The present study included 6938 women who were part of the first-year entry cohort for the fifth wave of the biannual follow-up survey of the JNHS. INTERVENTION: The participants were randomly allocated into four groups; Group-1 (business-reply, newsletter with initial mailing), Group-2 (business-reply, newsletter with reminder), Group-3 (stamped envelopes, newsletter with initial mailing) and Group-4 (stamped envelopes, newsletter with reminder). The thank-you and reminder letters were mailed out at the end of the sixth week. This study was censored at the end of 12 weeks. MAIN OUTCOME MEASURES: Main outcome measures were cumulative response at the end of 6 and 12 weeks after mailing out the questionnaire. RESULTS: The cumulative response at 12 weeks were 58.3% for Group-1, 54.1% for Group-2, 60.5% for Group-3 and 56.7% for Group-4 (p=0.001). The odds of the response was higher for stamped envelopes than for business-reply envelopes (OR (95% CI)=1.10(1.00 to 1.21)). The odds was higher for newsletter delivery with initial mailing than for with reminder (1.18(1.07 to 1.29)). The response in first 6 weeks for stamped envelope was significantly higher than for business-reply envelope (p=0.047). Although the response in 6 weeks for women received the newsletter with initial mailing was lower than for women who did not, the proportions did not differ significantly (p=0.291). CONCLUSIONS: The style of return envelope affected response rates of mail survey. The results of this study suggest that practices of provision of the additional information, should be handled individually in advance, as a separate event from sending follow-up questionnaire or reminder letters.