Research paper · RP10

The Thank-You Letter Effect

Does delivering gratitude to a person outperform writing it privately? A pooled expressed-minus-recorded Hedges g is not yet possible, so the number we can defend is Kirca, Malouff and Meynadier (2023): expressed gratitude versus a neutral control, g = 0.22, 95% CI [0.11, 0.33], from 25 randomised samples and 6,745 adults. Fewer than five eligible adult trials isolate delivered thanks versus private journaling with extractable effects, so this paper is a PRISMA-informed systematic review with narrative synthesis, not a new meta-analysis. That g = 0.22 estimate mixes delivered letters, unsent letters and mixed-intent writing. Inside the same review, whether the letter had reached the recipient before post-test did not moderate expresser wellbeing (Q(2) = 0.30, p = .86; delivered g = 0.19). Head-to-head trials tell a split story. One Irish trial found that adding a weekly thank-you to a gratitude journal improved affect balance and lowered low-mood scores at three weeks. A United States trial of 916 students found that a private unsent letter already lifted positive affect (partial d = 0.29) and life satisfaction (partial d = 0.17); texting the benefactor added connectedness (partial d = 0.18), not extra happiness. Recipients, measured separately, feel more positive than expressers predict (d = 0.74). Indian and other collectivist samples show smaller or null state-gratitude effects and more indebtedness. For an Indian workplace programme the honest product is a short written thank-you, optionally sent on WhatsApp to a person of the writer’s choice, never mandated up the hierarchy. Certainty is moderate for a small expressed-versus-control effect on expresser wellbeing and very low for any incremental happiness from delivery.