Combining Internet-Based and Postal Survey Methods in a Survey among Gynecologists: Results of a Randomized Trial

To assess whether a combination of Internet-based and postal survey methods (mixed-mode) compared to postal-only survey methods (postal-only) leads to improved response rates in a physician survey, and to compare the cost implications of the different recruitment strategies.

All primary care gynecologists in Bremen and Lower Saxony, Germany, were invited to participate in a cross-sectional survey from January to July 2014.

The sample was divided into two strata (A; B) depending on availability of an email address. Within each stratum, potential participants were randomly assigned to mixed-mode or postal-only group.

In Stratum A, the mixed-mode group had a lower response rate compared to the postal-only group (12.5 vs. 20.2 percent; RR = 0.61, 95 percent CI: 0.44-0.87). In stratum B, no significant differences were found (15.6 vs. 16.2 percent; RR = 0.95, 95 percent CI: 0.62-1.44). Total costs (in €) per valid questionnaire returned (Stratum A: 399.72 vs. 248.85; Stratum B: 496.37 vs. 455.15) and per percentage point of response (Stratum A: 1,379.02 vs. 861.02; Stratum B 1,116.82 vs. 1,024.09) were higher, whereas variable costs were lower in mixed-mode compared to the respective postal-only groups (Stratum A cost ratio: 0.47, Stratum B cost ratio: 0.71).

In this study, primary care gynecologists were more likely to participate by traditional postal-only than by mixed-mode survey methods that first offered an Internet option. However, the lower response rate for the mixed-mode method may be partly due to the older age structure of the responding gynecologists. Variable costs per returned questionnaire were substantially lower in mixed-mode groups and indicate the potential for cost savings if the sample population is sufficiently large.