Research paper · RP42

Messaging as the Medium

Messaging channels have been pooled for health behaviour. They have not been pooled for emotional wellbeing. This PRISMA-2020 systematic review and random-effects meta-analysis asked what SMS-, WhatsApp- and similar-messaging programmes deliver for adult wellbeing and stress, and what retention they hold. Ten randomised or controlled trials (about 5,225 adults, 2012–2024) met criteria and yielded an extractable effect size. The pooled Hedges g was 0.18 (95% CI 0.08 to 0.27). Heterogeneity was substantial (I² = 64%; τ² = 0.012). The 95% prediction interval ran from −0.10 to 0.46 and included no effect. A wellbeing-only subset was smaller still (g = 0.10). Stress and distress effects were larger (g = 0.26) but driven in part by two small clinical SMS pilots. One-way scheduled messages and two-way chat or group formats did not differ cleanly. High-income and low- and middle-income trials produced similar averages on sparse data. Retention is the clearer number. Median completion at the primary endpoint was about 80%. One-way daily or near-daily broadcasts held 85–93% of starters. Two-way conversational agents held as few as 42%. No completed Indian adult trial delivered a wellbeing or stress programme primarily by SMS or WhatsApp. Certainty is low for wellbeing, low for stress and distress, and moderate for one-way retention. A null workplace LINE programme of 1,021 employees sits inside the pool and is part of the result, not an inconvenience. Messaging is a distribution system, not magic. It keeps people in the room. What they practise in the room still has to be specified, counted and tested in India.