Bah humbug! Association between sending Christmas cards to trial participants and trial retention: randomised study within a trial conducted simultaneously across eight host trials.
Coleman E, Arundel C, Clark L, Doherty L, Gillies K, Hewitt C, Innes K, Parker A, Torgerson D, Treweek S. 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. 2021 12 14; 375:e067742.