Are there missing randomized trials in Cochrane systematic reviews and what is their impact on the results?: A methodological study
2Pontifical Catholic University of Chile, Chile
3Department of Health Research Methods, Evidence, and Impact, McMaster University, Canada
BACKGROUND Due to reproducibility, reliability and exhaustiveness, systematic reviews (SRs) are considered the best type of evidence synthesis to inform decision making, which is why the development of SRs increases every year. Because of this, it is possible to find several SRs answering the same question. Unfortunately, the primary studies identified and the results presented by reviews answering the same question may differ between them and mislead the decision making process. Cochrane systematic reviews (CSRs) are considered high quality due to their methodological rigor. In this study, we want to evaluate if CSRs miss any relevant primary studies. Moreover, we want to know if including any missed studies could have modified the results. OBJECTIVE To evaluate if CSRs incorporate all randomized trials and the impact of missing studies on the results, specifically on key messages, certainty of the evidence and magnitude of effects on their results. METHODS We will include a random sample of 150 CSRs published last year (2022) that addressed an intervention question. To create a reference standard composed of all the randomized trials addressing the question of each CSR, we will also search for all other non-CSR that answered the same question and create a list of all eligible trials in all reviews. We will use this reference standard to determine if CSRs missed any studies. Then, among CSRs that missed studies, we will incorporate the missing studies to the meta-analyses and evaluate their impact on the results of the CSRs, specifically key messages (according to GRADE Guideline methodology 26), certainty of evidence and magnitude of effects. RESULTS This project is in progress. We will describe how many CSRs missed studies, how many studies were missed and how many of CSRs that modified their conclusions in key messages, certainty of evidence and magnitude of effects. CONCLUSIONS The results of this project could impact the processes of developing evidence synthesis to ensure the completeness of CSRs. In addition, we could validate the reliability in CSR for guideline development and decision making. Optimizing and improving evidence synthesis processes allow to inform better stakeholders, including patients.