What survives
All ten practices, each with its measured effect size printed in the chapter rather than in an appendix. Implementation intentions are the strongest; expressive writing and behavioural activation are close behind.
What does not
The magnitude claimed in popular versions of every one of these. Gratitude journalling works, and it works about a fifth as well as the books that sell it imply. This volume prints the post-replication numbers.
Pennebaker and Beall (1986)
Journal of Abnormal Psychology 95(3) · 46 students
Tested Four sessions of fifteen minutes writing about a difficult experience
Found Fewer health-centre visits over the following six months
Since Among the most replicated small interventions in psychology, though meta-analytic effect sizes are modest — around d = 0.15 to 0.20 — rather than the dramatic figures often quoted
Davis, Choe, Meyers et al. (2016)
Journal of Counseling Psychology 63(1)
Tested Gratitude interventions against active controls, meta-analysis
Found Small effects versus measurement-only controls and smaller still versus active controls; benefit concentrated in people low at baseline
Since This is the careful synthesis, and it is well below the popular claims
Goldberg, Tucker, Greene et al. (2018)
Clinical Psychology Review 59 · 142 randomised trials
Tested Mindfulness-based interventions across 142 randomised trials
Found Comparable to established evidence-based treatments; superior to no treatment; not superior to other active treatments
Since This is the replication-aware synthesis
Gollwitzer and Sheeran (2006)
Advances in Experimental Social Psychology 38 · 94 studies reviewed
Tested Implementation intentions — specifying when, where and how — meta-analysis of 94 studies
Found Medium-to-large effect on goal attainment, d = 0.65
Since Yes; one of the more robust findings in behaviour change
What would change this rating
A failure of the implementation-intention literature under pre-registration would move this rung materially, since that finding carries several of the ten.
A rating that no possible finding could
alter is an opinion. Every volume names the result that
would move it.