Slide 1: Do you know…? What is publication bias?
Slide 2: Publication Bias. The failure to publish results of studies on the basis of the direction or strength of the study findings. How can we assess whether publication bias is at play in a body of literature?
Slide 3: Funnel Plots. A simple graphical test for publication bias. Larger trials with narrow confidence intervals (higher precision) are more likely to be closer to the actual effect size. Smaller trials with wider confidence intervals are more heterogenous due to random error.
A body of literature without publication bias should have smaller trials evenly distributed at the base of the triangle and larger trials close together at the point.
Graphic of funnel plot. Study precision (sample size) on the y axis. Study result (effect size) on the x axis.
Slide 4: A real life example. This is a meta-analysis of clinical trials of aspirin for prevention of pre-eclampsia. Despite many small trials showing a benefit to aspirin, the largest one (CLASP) failed to show a benefit, suggesting the presence of publication bias in the literature. These trials were never published!
- Dickersin K, Min YI. Publication bias: the problem that won’t go away. Ann N Y Acad Sci. 1993 Dec 31;703:135-46; discussion 146-8. PMID 8192291.
- Murad MH, Montori VM, Ioannidis JP, Jaeschke R, Devereaux PJ, Prasad K, Neumann I, Carrasco-Labra A, Agoritsas T, Hatala R, Meade MO, Wyer P, Cook DJ, Guyatt G. How to read a systematic review and meta-analysis and apply the results to patient care: users’ guides to the medical literature. JAMA. 2014 Jul;312(2):171-9. PMID 25005654.
- Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ. 1997 Sep 13;315(7109):629-34. PMID 9310563.
Tags: funnel plot, publication bias, statistics