Text message reminders to improve questionnaire response rates

To assess whether short message service (SMS) text messages sent as prenotification or postnotification reminders improve questionnaire response rates in randomized controlled trial (RCT) follow-up.

Three "trials within a trial" assessed text message notifications sent before or after receipt of a follow-up questionnaire within an RCT for patients with depression. Consenting patients (n = 523) were randomized to receive a prenotification or no notification at 3 months, prenotification or postnotification at 6 months, and a postnotification or no notification at 12-month follow-up. Unadjusted and adjusted questionnaire return rates and time to return were compared.

The two trials comparing prenotification or postnotification with no notification at 3- and 9-month follow-up found no evidence of an effect on questionnaire response rates (3-month response rate: 82.9% vs. 84.7% (difference 1.79%, 95% confidence interval [CI] -4.53% to 8.11%, P = 0.58); 9-month response rate: 77.1% vs. 78.5% (difference = -1.44%, 95% CI -8.56% to 5.67%, P = 0.69). For the trial at 6-month follow-up, there was a statistically significant difference in response rates for postnotification (83.2%) compared with prenotification (75.2%), (difference 7.95%, 95% CI 1.00% to 14.91%, P = 0.02).

SMS as a prenotification device seems ineffective. For postnotification, the evidence is unclear.