PainSci summary of Pereira 2012?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided at the bottom of the page, as often as possible. ★★★★☆?4-star ratings are for bigger/better studies and reviews published in more prestigious journals, with only quibbles. Ratings are a highly subjective opinion, and subject to revision at any time. If you think this paper has been incorrectly rated, please let me know.
A “very large effect” in medical research is probably exaggerated, according to Stanford researchers. Small trials of medical treatments often produce results that seem impressive. However, when more and better trials are performed, the results are usually much less promising. In fact, “most medical interventions have modest effects” and “well-validated large effects are uncommon.”
original abstract†Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
CONTEXT: Most medical interventions have modest effects, but occasionally some clinical trials may find very large effects for benefits or harms.
OBJECTIVE: To evaluate the frequency and features of very large effects in medicine.
DATA SOURCES: Cochrane Database of Systematic Reviews (CDSR, 2010, issue 7).
STUDY SELECTION: We separated all binary-outcome CDSR forest plots with comparisons of interventions according to whether the first published trial, a subsequent trial (not the first), or no trial had a nominally statistically significant (P < .05) very large effect (odds ratio [OR], ≥5). We also sampled randomly 250 topics from each group for further in-depth evaluation.
DATA EXTRACTION: We assessed the types of treatments and outcomes in trials with very large effects, examined how often large-effect trials were followed up by other trials on the same topic, and how these effects compared against the effects of the respective meta-analyses.
RESULTS: Among 85,002 forest plots (from 3082 reviews), 8239 (9.7%) had a significant very large effect in the first published trial, 5158 (6.1%) only after the first published trial, and 71,605 (84.2%) had no trials with significant very large effects. Nominally significant very large effects typically appeared in small trials with median number of events: 18 in first trials and 15 in subsequent trials. Topics with very large effects were less likely than other topics to address mortality (3.6% in first trials, 3.2% in subsequent trials, and 11.6% in no trials with significant very large effects) and were more likely to address laboratory-defined efficacy (10% in first trials,10.8% in subsequent, and 3.2% in no trials with significant very large effects). First trials with very large effects were as likely as trials with no very large effects to have subsequent published trials. Ninety percent and 98% of the very large effects observed in first and subsequently published trials, respectively, became smaller in meta-analyses that included other trials; the median odds ratio decreased from 11.88 to 4.20 for first trials, and from 10.02 to 2.60 for subsequent trials. For 46 of the 500 selected topics (9.2%; first and subsequent trials) with a very large-effect trial, the meta-analysis maintained very large effects with P < .001 when additional trials were included, but none pertained to mortality-related outcomes. Across the whole CDSR, there was only 1 intervention with large beneficial effects on mortality, P < .001, and no major concerns about the quality of the evidence (for a trial on extracorporeal oxygenation for severe respiratory failure in newborns).
CONCLUSIONS: Most large treatment effects emerge from small studies, and when additional trials are performed, the effect sizes become typically much smaller. Well-validated large effects are uncommon and pertain to nonfatal outcomes.
These four articles on PainScience.com cite Pereira 2012 as a source:
- PS The “Impress Me” Test — Most controversial therapies are fighting over scraps of “positive” evidence that damn them with faint praise
- PS Ioannidis: Making Medical Science Look Bad Since 2005 — A famous and excellent scientific paper … with an alarmingly misleading title
- PS Statistical Significance Abuse — A lot of research makes scientific evidence seem more “significant” than it is
- PS Science versus Experience in Musculoskeletal Medicine — The conflict between science and clinical experience and pragmatism in the management of aches, pains, and injuries
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- A Bayesian model-averaged meta-analysis of the power pose effect with informed and default priors: the case of felt power. Gronau 2017 Comprehensive Results in Social Psychology.
- Association of Spinal Manipulative Therapy With Clinical Benefit and Harm for Acute Low Back Pain: Systematic Review and Meta-analysis. Paige 2017 JAMA.
- Incidence of Spontaneous Resorption of Lumbar Disc Herniation: A Meta-Analysis. Zhong 2017 Pain Physician.
- How much is too much? (Part 1) International Olympic Committee consensus statement on load in sport and risk of injury. Soligard 2016 Br J Sports Med.
- Chiropractic spinal manipulative therapy for migraine: a three-armed, single-blinded, placebo, randomized controlled trial. Chaibi 2016 Eur J Neurol.