Should I include studies from "predatory" journals in a systematic review? Interim guidance for systematic reviewers

A systematic review involves the identification, evaluation, and synthesis of the best-available evidence to provide an answer to a specific question. The "best-available evidence" is, in many cases, a peer-reviewed scientific article published in an academic journal that details the conduct and results of a scientific study. Any potential threat to the validity of these individual studies (and hence the resultant synthesis) must be evaluated and critiqued. In science, the number of predatory journals continue to rise. Studies published in predatory journals may be of lower quality and more likely to be impacted by fraud and error compared to studies published in traditional journals. This poses a threat to the validity of systematic reviews that include these studies and, therefore, the translation of evidence into guidance for policy and practice. Despite the challenges predatory journals present to systematic reviewers, there is currently little guidance regarding how they should be managed. In 2020, a subgroup of the JBI Scientific Committee was formed to investigate this issue. In this overview paper, we introduce predatory journals to systematic reviewers, outline the problems they present and their potential impact on systematic reviews, and provide some alternative strategies for consideration of studies from predatory journals in systematic reviews. Options for systematic reviewers could include excluding all studies from suspected predatory journals, applying additional strategies to forensically examine the results of studies published in suspected predatory journals, setting stringent search limits, and applying analytical techniques (such as subgroup or sensitivity analyses) to investigate the impact of suspected predatory journals in a synthesis.