Abstract
BackgroundLow participation rates are one of the most serious disadvantages of Web-based studies. It is necessary to develop effective strategies to improve participation rates to obtain sufficient data.ObjectiveThe objective of this trial was to investigate the effect of emphasizing the incentive in the subject line of the invitation email and the day of the week of sending the invitation email on the participation rate in a Web-based trial.MethodsWe conducted a 2×2 factorial design randomized controlled trial. We contacted 2000 primary care physicians from members of the Japan Primary Care Association in January 2017 and randomly allocated them to 1 of 4 combinations of 2 subject lines (presence or absence of an emphasis on a lottery for an Amazon gift card worth 3000 yen or approximately US $30) and 2 delivery days (sending the invitation email on Tuesday or Friday). The primary outcome was the response rate defined as the number of participants answering the first page of the questionnaire divided by the number of invitation emails delivered. All outcomes were collected between January 17, 2017, and February 8, 2017.ResultsWe analyzed data from 1943 out of 2000 participants after excluding those whose email addresses were invalid. The overall response rate was 6.3% (123/1943). There was no significant difference in the response rates between the 2 groups regarding incentive in the subject line: the risk ratio was 1.12 (95% CI 0.80 to 1.58) and the risk difference was 0.7% (95% CI –1.5% to 2.9%). Similarly, there was no significant difference in the response rates between the 2 groups regarding sending the email on Tuesday or Friday: the risk ratio was 0.98 (95% CI 0.70 to 1.38) and the risk difference was –0.1% (95% CI –2.3% to 2.1%).ConclusionsNeither emphasizing the incentive in the subject line of the invitation email nor varying the day of the week the invitation email was sent led to a meaningful increase in response rates in a Web-based trial with primary care physicians.Trial RegistrationUniversity Hospital Medical Information Network Clinical Trials Registry UMIN000025317; https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000029121 (Archived by WebCite at http://www.webcitation. org/6wOo1jl9t)
Highlights
MethodsOne of the most serious drawbacks of Web-based studies is their considerably smaller participation rates compared to paper-based studies [1,2], even though Web-based studies are widely used to explore clinicians’ knowledge, perspectives, and clinical practice [3,4,5]
There was no significant difference in the response rates between the 2 groups regarding incentive in the subject line: the risk ratio was 1.12 and the risk difference was 0.7%
Neither emphasizing the incentive in the subject line of the invitation email nor varying the day of the week the invitation email was sent led to a meaningful increase in response rates in a Web-based trial with primary care physicians
Summary
MethodsOne of the most serious drawbacks of Web-based studies is their considerably smaller participation rates compared to paper-based studies [1,2], even though Web-based studies are widely used to explore clinicians’ knowledge, perspectives, and clinical practice [3,4,5]. Incentives, contact timing, content of subject line and message of invitation emails, length of questionnaire, survey webpage design, and individualization among others were proposed as factors that may improve participation rates of Web-based studies [6,7,8]. Objective: The objective of this trial was to investigate the effect of emphasizing the incentive in the subject line of the invitation email and the day of the week of sending the invitation email on the participation rate in a Web-based trial. Conclusions: Neither emphasizing the incentive in the subject line of the invitation email nor varying the day of the week the invitation email was sent led to a meaningful increase in response rates in a Web-based trial with primary care physicians. Trial Registration: University Hospital Medical Information Network Clinical Trials Registry UMIN000025317; https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000029121 (Archived by WebCite at http://www.webcitation. org/6wOo1jl9t)
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