How large are positive psychology interventions, really?
Linda Bolier and colleagues · Positive Psychology Interventions: A Meta-Analysis of Randomized Controlled Studies, BMC Public Health 13 · 2013
A · Replicated at scale
Across 39 randomised studies, positive psychology interventions produced small effects on subjective wellbeing, standardised mean difference about 0.34, and on psychological wellbeing about 0.20, with a smaller effect on depression. Effects were heterogeneous and often measured against weak controls. Small and real is the correct reading.
ProbeBefore starting a practice, write the effect size you expect and how you will measure it in yourself. Then measure.