Coleman, ElizabethArundel, CatherineClark, LauraDoherty, LauraGillies, KatieHewitt, Catherine AInnes, KarenParker, AdwoaTorgerson, DavidTreweek, Shaun2021-12-142021-12-142021-12-14Coleman, E, Arundel, C, Clark, L, Doherty, L, Gillies, K, Hewitt, C A, Innes, K, Parker, A, Torgerson, D & Treweek, S 2021, 'Bah humbug! Association between sending Christmas cards to trial participants and trial retention : randomised study within a trial conducted simultaneously across eight host trials', BMJ, vol. 375, e067742. https://doi.org/10.1136/bmj-2021-0677420959-8146ORCID: /0000-0001-7890-2854/work/104792265ORCID: /0000-0001-8512-4368/work/104792577ORCID: /0000-0002-7239-7241/work/186968498https://hdl.handle.net/2164/17680We 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.101201368engSDG 3 - Good Health and Well-beingR MedicineMedical Research Council (MRC)MR/R013748/1Cancer Research UKNational Institute for Health Research (NIHR)RJournal article10.1136/bmj-2021-067742375