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.