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

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.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.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.Although response rates vary by study and mode of administration, there is evidence that response rates are declining across all modes of survey administration [1-3]. Mixed mode surveys have been shown to increase response rates by appealing to respondents who did not respond to the first mode they were offered [4]. Thus switching modes can offer potential respondents an additional opportunity for survey completion and allow respondents to complete the survey utilizing a mode with which they may feel more comfortable.Dillman and colleagues [5] suggest making the final contact to a potential respondent distinct from previous failed attempts as a way to increase response rates based on the premise that people prefer di