Publication bias in psychological science: prevalence, methods for identifying and controlling, and implications for the use of meta-analyses.

The issue of publication bias in psychological science is one that has remained difficult to address despite decades of discussion and debate. The current article examines a sample of 91 recent meta-analyses published in American Psychological Association and Association for Psychological Science journals and the methods used in these analyses to identify and control for publication bias. Of the 91 studies analyzed, 64 (70%) made some effort to analyze publication bias, and 26 (41%) reported finding evidence of bias. Approaches to controlling publication bias were heterogeneous among studies. Of these studies, 57 (63%) attempted to find unpublished studies to control for publication bias. Nonetheless, those studies that included unpublished studies were just as likely to find evidence for publication bias as those that did not. Furthermore, authors of meta-analyses themselves were overrepresented in unpublished studies acquired, as compared with published studies, suggesting that searches for unpublished studies may increase rather than decrease some sources of bias. A subset of 48 meta-analyses for which study sample sizes and effect sizes were available was further analyzed with a conservative and newly developed tandem procedure of assessing publication bias. Results indicated that publication bias was worrisome in about 25% of meta-analyses. Meta-analyses that included unpublished studies were more likely to show bias than those that did not, likely due to selection bias in unpublished literature searches. Sources of publication bias and implications for the use of meta-analysis are discussed.