SMS text pre-notification and delivery of reminder e-mails to increase response rates to postal questionnaires: a factorial design, randomised, controlled trial

Methods We evaluated two interventions aimed at increasing postal questionnaire response rates in a 2x2 partial factorial RCT nested within a single, large, UK-wide RCT of medical expulsive therapy for ureteric stones. The interventions were: questionnaire pre-notification via SMS text prior to posting the trial questionnaires versus no pre-notification; for non-responders to the initial questionnaire mailing, use of an e-mail reminder (containing a hyperlink for online questionnaire completion) versus a postal reminder with paper questionnaire. Participants were randomised to the pre-notification comparison, the reminder comparison or both, depending on whether they supplied mobile telephone number and/or email address. The primary outcome was response to 4 and 12 week questionnaires.