E-mail invitations to general practitioners were as effective as postal invitations and were more efficient

ObjectiveTo evaluate which of two invitation methods, e-mail or post, was most effective at recruiting general practitioners (GPs) to an online trial.Study Design and SettingRandomized controlled trial. Participants were GPs in Scotland, United Kingdom.ResultsTwo hundred and seventy GPs were recruited. Using e-mail did not improve recruitment (risk difference = 0.7% [95% confidence interval −2.7% to 4.1%]). E-mail was, however, simpler to use and cheaper, costing £3.20 per recruit compared with £15.69 for postal invitations. Reminders increased recruitment by around 4% for each reminder sent for both invitation methods.ConclusionsIn the Scottish context, inviting GPs to take part in an online trial by e-mail does not adversely affect recruitment and is logistically easier and cheaper than using postal invitations.