The effect of reminders in a web-based intervention study

Knowledge on effective strategies to encourage participation in epidemiological web-based research is scant. We studied the effects of reminders on overall participation. 3,876 employees were e-mailed a baseline web-based lifestyle questionnaire. Nine months later, a follow-up questionnaire was sent. To encourage study participation, 4—5 and 11 e-mail reminders were sent at baseline and follow-up, respectively. Additional reminders (media articles, flyers, SMS etc) were also administered. Reminders (e-mails + additional) were given in low (≤6 reminders), medium (7—9 reminders) or high amounts (>9 reminders). Participation was examined with respect to participant characteristics (i.e. age, sex, Body Mass Index, occupation), type/number of reminders, and time of participation. Most participants were males, 35—49 years, and field workers (non-office based). About 29 % responded before any e-mail reminder, following 26 and 45 % after 1 respective ≥ 2 e-mail reminders. Participant characteristics were not related to when the participants responded. The 4—5 e-mail reminders increased total response rate by 15 %, the eleven by 21 % (greatest increases in September). Those receiving medium amounts of reminders (reference) had the highest response rate (75 %), likewise office workers (54 %) compared to field workers (33 %). High amounts of reminders were particularly effective on office workers. The participants' characteristics were not related to when they responded in this web-based study. Frequent reminders were effective on response rates, especially for those with high Internet availability. The highest increases in response rates were found in September.