Telephone follow-up to a mail survey: when to offer an interview compared to a reminder call

BACKGROUND: Using a different mode of contact on the final follow-up to survey non-respondents is an identified strategy to increase response rates. This study was designed to determine if a reminder phone call or a phone interview as a final mode of contact to a mailed survey works better to increase response rates and which strategy is more cost effective. METHODS: A randomized study was embedded within a survey study of individuals treated with ulcerative colitis conducted in March 2009 in Olmsted County, Minnesota. After two mail contacts, non-respondents were randomly assigned to either a reminder telephone call or a telephone interview. Average cost per completed interview and response rates were compared between the two experimental conditions. RESULTS: The response rate in the reminder group and the interview did not differ where we considered both a completed survey and a signed form a complete (24% vs. 29%, p = 0.08). However, if such a signed form was not required, there was a substantial advantage to completing the interview over the phone (24% vs. 43%, p < 0.0001). The reminder group on average cost $27.00 per completed survey, while the interview group on average cost $53.00 per completed survey when a signed form was required and $36.00 per complete when a signed form was not required. CONCLUSIONS: The additional cost of completing an interview is worth it when an additional signed form is not required of the respondent. However, when such a signed form is required, offering an interview instead of a reminder phone call as a follow up to non-respondents does not increase response rates enough to outweigh the additional costs.