Conclusions
The use of an emailed approach and online completion avoids printing and postage costs and the costs of manual data entry for those who responded to the second reminder. However, the lower response rates means that costs increase for the third mailed reminder as a higher number of participants needed to be approached. It remains unclear what advice to provide researchers as one might be willing to accept a lower response rate if costs are also lower. Often budgets for such surveys are very limited and email is the only option. In this case, optimising other survey characteristics (e.g. survey length) that can increase response rates is important using existing evidence [We thank the doctors who participated in the MABEL survey.