Contacting authors by telephone increased response proportions compared with emailing: results of a randomized study

The aim of the study was to compare response proportions and research costs of telephone calling vs. continued emailing nonresponding authors of studies included in a systematic review.

Key features of included studies were poorly reported in a systematic review of diabetes quality improvement interventions. We developed a survey to request additional information from contact authors. After three email contact attempts, only 76 of 279 authors (27%) had completed the survey. In this study, we randomly assigned nonresponding authors to contact by telephone calling vs. continued emailing to compare the effect of these strategies on response proportions and research costs.

We randomized 87 authors to telephone and 89 to email contact. Telephone contact increased survey completion (36.7% vs. 20.2%; adjusted risk difference of 15.6% [95% confidence interval: 2.90%, 28.4%]; adjusted odds ratio 2.26 [95% confidence interval: 1.10, 4.76]) but required more time to deliver (20 vs. 10 hours in total; 14 vs. 7 minutes per randomized author; 26 vs. 4 weeks), and cost more (total intervention cost of $504 Canadian dollars vs. $252 for the telephone and email arm, respectively).

Contacting nonresponding authors of included studies by telephone increased response compared with emailing but required more investigator time and had higher cost.