Source
Sheeran, Listrom & Gollwitzer, LIT-1488, read in full in NOTE-1131 from the version of record in KOPS: pp. 168–173, Tables 1 and 2, and p. 183.
What was actually shown
- Pooled (p. 170). d = .36 [.33, .40] over 642 tests from 294 reports, experimental designs only.
- Bias (p. 170). Egger’s regression b = 1.06, above the threshold for “substantial” bias; trim and fill .35; robust Bayesian meta-analysis: extreme evidence for an effect, for publication bias and for heterogeneity, model-averaged d = .15 [.08, .22]. “Thus, implementation intentions appear to have a robust impact on outcomes though the effect size is small according to conventional guidelines” (p. 170).
- By outcome (Table 1, p. 171). Behaviour .27 (k = 301), cognitive performance .47 (k = 204), affect regulation .66 (k = 26), social judgement .52 (k = 20). Vaccination and voting did not differ reliably from zero.
- By setting (Table 2). Lab .49, field .27; in person .53, online .31; objective outcomes .43, self-report .28.
What could have come out otherwise: the bias correction could have left no effect, as it has for some behavioural interventions in the debate the authors cite (p. 170).
What this does not say
- That the per-outcome figures are corrected. Only the overall estimate was corrected; Tables 1–4 are uncorrected.
- That the effect is up to date. The search ends in September 2019 and was not updated (p. 168).
- How plans work. No mechanism was tested in this review.
- That the 2006 estimate was wrong in kind. The two sets differ in inclusion (2024 excludes correlational designs and includes schedule plans and non-behavioural outcomes), so the comparison of .65 with .36 is not like for like.
Connections
- CLAIM-443. The claim grounds part of its case on implementation intentions. The reliable existence of the effect supports the premise that pre-arranged situation–response links change what people do; the small corrected size is a reason not to cite it as large.
- THEORY-913 holds the 2006 process evidence, which this review does not re-test.