This problem is addressed in PRISMA 2009, PRISMA 2020 and MECIR. Some missing outcome data is expected in most systematic reviews due to reporting biases or word count restrictions in published papers therefore systematic review authors should plan how they will deal with missing outcome data. For example, contacting study authors or imputation. The Risk Of Bias due to Missing Evidence in a synthesis (ROB-ME) is a tool for this scenario.
Articles that support this problem:
Can Cochrane Reviews in controversial areas be biased? A sensitivity analysis based on the protocol of a Systematic Cochrane Review on low-level laser therapy in osteoarthritis
2005 : Photomedicine and laser therapy
Reporting, handling and assessing the risk of bias associated with missing participant data in systematic reviews: a methodological survey
2015 : Bmj open
Can a core outcome set improve the quality of systematic reviews?–a survey of the Co-ordinating Editors of Cochrane Review Groups
2013 : Trials
Effects of drop-out on efficacy estimates in five Cochrane reviews of popular antipsychotics for schizophrenia
2012 : Acta psychiatrica scandinavica
Reporting and handling missing outcome data in mental health: a systematic review of Cochrane systematic reviews and meta‐analyses
2015 : Research synthesis methods
Missing binary data extraction challenges from Cochrane reviews in mental health and Campbell reviews with implications for empirical research
2017 : Research synthesis methods
Contacting of authors modified crucial outcomes of systematic reviews but was poorly reported, not systematic, and produced conflicting results
2019 : Journal of clinical epidemiology
A systematic survey shows that reporting and handling of missing outcome data in networks of interventions is poor
2018 : Bmc medical research methodology
Systematic reviews do not adequately report or address missing outcome data in their analyses: a methodological survey
2018 : Journal of clinical epidemiology
Systematic reviewers commonly contact study authors but do so with limited rigor
2009 : Journal of clinical epidemiology
Potential impact of missing outcome data on treatment effects in systematic reviews: imputation study
2020 : Bmj
The impact of outcome reporting bias in randomised controlled trials on a cohort of systematic reviews
2010 : Bmj
Assessment of publication bias and outcome reporting bias in systematic reviews of health services and delivery research: A meta-epidemiological study
2020 : Plos one
Reporting and Handling of Missing Participant Data in Systematic Reviews of Kidney Transplant Studies
2021 : Transplantation
Improving prediction model systematic review methodology: Letter to the Editor
2021 : Translational sports medicine
Missing Data in Systematic Reviews and Meta-Analysis
2022 : Pediatric critical care medicine