Randomised study within a trial (SWAT) to evaluate personalised versus standard text message prompts for increasing trial participant response to postal questionnaires (PROMPTS)

Abstract

Background: Use of a person's name in a text message has been shown to be effective in instigating behaviour change. We evaluated the effectiveness of a personalised text message (including the recipient's name) versus a standardised text message for prompting a response from trial participants to complete and return postal follow-up questionnaires.

Methods: Using a randomised study within a trial (SWAT) embedded within the host GRASP (Getting it Right: Addressing Shoulder Pain) trial, participants who provided a mobile telephone number were randomised (1:1) by a central computer system to receive either (1) a personalised text message which included their name or (2) a standard text message. Text messages were sent by the trial office on the same day as the 6-month GRASP follow-up questionnaire. The primary outcome was questionnaire response rate, defined as the proportion of 6-month GRASP follow-up questionnaires returned by participants. Secondary outcomes included time to response, the proportion of participants sent a reminder follow-up questionnaire, and cost.

Results: Between March 2017 and May 2019 (recruitment period for GRASP trial), 618 participants were randomised to a personalised (n = 309) or standard (n = 309) text message and all were included in the analysis. The overall questionnaire response rate was 87% (n = 537/618); 90% (n = 277/309) of participants responded in the personalised text message group compared to 84% (n = 260/309) in the standard text message group (relative risk (RR) 1.07; 95% CI 1.00 to 1.13). Participants randomised to receive the personalised text message were more likely to return their initial postal questionnaire than those who received the standard text message (n = 185/309; 60% vs. n = 160/309; 52%) (RR 1.16; 95% CI 1.00 to 1.33); this represents an absolute percentage difference between intervention groups of 8%. Post hoc subgroup analysis showed that males under 65 years were the group most likely to return their initial questionnaire if they received a personalised text message.

Conclusion: Overall, participants who received a personalised text message were more likely to return their questionnaire than those who received the standard text message.

Trial registration: GRASP Trial ISRCTN16539266 ; SWAT Repository ID 35.

Keywords: Postal questionnaire; Randomised controlled trial; Retention; Study within a trial; Trial methodology.

Fig. 1

Flow diagram of participants at each stage. ¹Reasons for not receiving allocation: message not sent in error (n = 10), incorrect mobile number (n = 5), randomised in error (n = 4), and patient withdrawn from host trial (n = 3). ²Reasons for not receiving allocation: message not sent in error (n = 12), incorrect mobile number (n = 4), randomised in error (n = 2), and patient withdrawn from host trial (n = 2). Incorrect mobile number, participant provided 10 not 11 digit mobile telephone number

Fig. 2

Kaplan-Meier curves and log-rank test of time to overall response personalised and standard text messages (n = 618)

Fig. 3

Kaplan-Meier curves and log-rank test of time to response for initial questionnaire for personalised and standard text messages (n = 344)

Fig. 4

Personalised versus standard text message: overall questionnaire response rate

Fig. 5

Personalised versus standard text message: reminder questionnaire sent