Bah humbug! Association between sending Christmas cards to trial participants and trial retention: randomised study within a trial conducted simultaneously across eight host trials

Elizabeth Coleman, Catherine Arundel, Laura Clark, Laura Doherty, Katie Gillies, Catherine A Hewitt, Karen Innes, Adwoa Parker, David Torgerson, Shaun Treweek* (Corresponding Author)

*Corresponding author for this work

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Objectives To determine the effectiveness of sending Christmas cards to participants in randomised controlled trials to increase retention rate at follow-ups, and to explore the feasibility of doing a study within a trial (SWAT) across multiple host trials simultaneously.

Design Randomised SWAT conducted simultaneously across eight host trials.

Setting Eight randomised controlled trials researching various areas including surgery and smoking cessation.

Participants 3223 trial participants who were still due at least one follow-up from their host randomised controlled trial.

Intervention Participants were randomised (1:1, separately by each host trial) to either received a Christmas card in mid-December 2019 or to not receive a card.

Main outcome measure Proportion of participants completing their next follow-up (retention rate) within their host randomised controlled trial.

Results 1469 participants (age 16-94 years; 70% (n=1033) female; 96% (813/847) white ethnicity) across the eight host randomised controlled trials were involved in the analysis (cut short owing to covid-19). No evidence was found of a difference in retention rate between the two arms for any of the host trials when analysed separately or when the results were combined (85.3% (639/749) for cards versus 85.4% (615/720) for no card; odds ratio 0.96, 95% confidence interval 0.71 to 1.29; P=0.77). No difference was observed when comparing just participants who were due a follow-up in the 30 days after receiving the card (odds ratio 0.96, 0.42 to 2.21). No evidence of a difference in time to complete the questionnaire was found (hazard ratio 1.01, 95% confidence interval 0.91 to 1.13; P=0.80). These results were robust to post hoc sensitivity analyses. The cost of this intervention was £0.76 (€0.91; $1.02) per participant, and it will have a carbon footprint of approximately 140 g CO2 equivalent per card. One benefit of this approach was the need to only submit one ethics application.

Conclusions Sending Christmas cards to participants in randomised controlled trials does not increase retention. Undertaking a SWAT within multiple randomised controlled trials at the same time is, however, possible. This approach should be used more often to build an evidence base to support selection of recruitment and retention strategies. Although no evidence of a boost to retention was found, embedding a SWAT in multiple host trials simultaneously has been shown to be possible.
Original languageEnglish
Article numbere067742
Number of pages10
Early online date14 Dec 2021
Publication statusPublished - 14 Dec 2021

Bibliographical note

We acknowledge the host trial teams, and specifically members
who were involved in the implementation of this SWAT. These include Sally Baker, Katie Banister, Zoe Batham, Suzanne Breeman, Patrycja Bromm, Emma Brookes, Becky Bruce, Louise Campbell, Seonaidh Cotton, Janice Cruden, Tracey Davidson, Dianne Dejean, Charlotte Diamond, Anne Duncan, Maddy Elliot, Elerita Flammini, Mark Forrest, Andrea Fraser, Pauline Garden, Sue Heslop, Kalpita
Joshi, Amy Marshall, Dawn McRae, Alex Mitchell, Maria Ntessalen, Tanya Pawson, Lyn Robinson-Smith, Lesley Sinclair, Kath Starr, Bev Smith, Brian Taylor, Puvan Tharmanathan, Charlie Welch, and Sharon Wren. Additionally, we acknowledge the HSRU Patient and Public Involvement Group, which contributed to the Christmas card design

Funding: This study within a trial (SWAT) was funded by the PROMETHEUS MRC programme grant (MR/R013748/1). Each host trial received its own funding. C-Gall, DISC, FUTURE, ProFHER-2, PUrE, REFLECT, and SWHSI-2 were funded by the National Institute for Health Research Health Technology Assessment Programme. CPIT-3 was funded by Cancer Research UK, the Chief Scientist Office, Scottish Government, HSC Public Health Agency NI, Chest Heart and Stroke NI, The Lullaby Trust, Public Health Agency NI, and the Scottish Cot
Death Trust. The Health Services Research Unit (HSRU) is core funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorate. The funders (MRC) had no role in considering the study design or in the collection, analysis, or interpretation of the data; the writing of the report; or the decision to submit the article for publication.


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