This problem is addressed in AMSTAR 2, ROBIS and MECIR. Traditional meta-analyses are appropriate for synthesising the results of randomised controlled trials. Increasingly observational studies are included in systematic reviews which is not a problem in inself but these studies require interpretation with appropriate critical appraisal tools and data synthesis methods.
Articles that support this problem:
Quality assessment of observational studies is not commonplace in systematic reviews
2006 : Journal of clinical epidemiology
Risk of bias tools in systematic reviews of health interventions: an analysis of PROSPERO-registered protocols
2019 : Systematic reviews
Methodological quality and risk-of-bias assessments in systematic reviews of treatments for peri-implantitis
2019 : Journal of periodontal research
Use of methodological tools for assessing the quality of studies in periodontology and implant dentistry: a systematic review
2014 : Journal of clinical periodontology
Systematic reviews synthesized evidence without consistent quality assessment of primary studies examining epidemiology of chronic diseases
2012 : Journal of clinical epidemiology
Challenges in systematic reviews that assess treatment harms
2005 : Annals of internal medicine
The quality of systematic reviews about interventions for refractive error can be improved: a review of systematic reviews
2017 : Bmc ophthalmology
Risk of Bias in Systematic Reviews of Non-Randomized Studies of Adverse Cardiovascular Effects of Thiazolidinediones and Cyclooxygenase-2 Inhibitors: Application of a New Cochrane Risk of Bias Tool
2016 : Plos medicine
Inclusion of nonrandomized studies in Cochrane systematic reviews was found to be in need of improvement
2014 : Journal of clinical epidemiology
Results from a meta-analysis comparing bovine carotid artery grafts with polytetrafluoroethylene grafts must be interpreted with caution due to methodological flaws
2021 : Journal of vascular access
Cochrane's risk of bias tool for non-randomized studies (ROBINS-I) is frequently misapplied: A methodological systematic review
2021 : Journal of clinical epidemiology
Methodological issues in meta-analyses of observational studies: the need for attention to the details
2022 : British journal of anaesthesia