Accuracy of Effect Size Estimates from Published Psychological Research

A Monte-Carlo simulation was used to model the biasing of effect sizes in published studies and indicates that, when a predominant bias to publish studies with statistically significant results is coupled with inadequate statistical power, there will be an overestimation ofeffect sizes.

Abstract

A Monte-Carlo simulation was used to model the biasing of effect sizes in published studies. The findings from the simulation indicate that, when a predominant bias to publish studies with statistically significant results is coupled with inadequate statistical power, there will be an overestimation of effect sizes. The consequences such an effect size overestimation will then have on meta-analyses and power analyses are highlighted and discussed along with measures which can be taken to reduce the problem.