The impact of phone calls on follow-up rates in an online depression prevention study.

•The study examined whether phone calls improved follow-up rates beyond email reminders and financial incentives.•Consented participants were randomized to either a Call or a No Call condition.•Those in the Call condition received phone calls if they did not complete the surveys in response to email reminders.•The Call condition yielded higher completion rates at each follow-up period, but findings did not reach significance.•Response to follow-up was low and the number of phone calls required raises concerns about the utility of adding phone calls.