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

Objective: To 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 Setting: Randomized controlled trial. Participants were GPs in Scotland, United Kingdom. Results: Two 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. Conclusions: In 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.