Supplementary Material for: Methodological quality of systematic reviews on treatments for gastric cancer: a cross-sectional study

Introduction: Systematic reviews (SRs) provide crucial evidence for gastric cancer interventions, but their reliability can be compromised by methodological flaws. We aimed to evaluate the methodological quality of SRs on gastric cancer interventions and identify factors affecting their quality.
Methods: We searched MEDLINE, APA PsycInfo, Embase, and Cochrane Database of SRs for eligible SRs published between January 2014 and October 2023. The methodological quality was assessed using AMSTAR 2. Multivariable regression analyses were conducted to identify factors influencing quality.
Results: Among 119 identified SRs (including 1,305 RCTs with 233,197 participants), only 2.5% were rated as high quality, while 89.1% were critically low quality. Higher journal impact factor was associated with better performance in addressing heterogeneity (AOR: 1.37, 95% CI: 1.02-1.84), investigating publication bias (AOR: 1.41, 95% CI: 1.03-1.94), reporting conflicts of interest (AOR: 2.85, 95% CI: 1.59-5.11), and establishing protocols (AOR: 3.33, 95% CI: 1.89-5.87). More review authors predicted better statistical methods (AOR: 1.20, 95% CI: 1.03-1.40) and protocol establishment (AOR: 1.31, 95% CI: 1.06-1.63). Recent publications showed improved conflict of interest reporting (AOR: 1.54, 95% CI: 1.09-2.10) and risk of bias assessment (AOR: 1.34, 95% CI: 1.03-1.75). Non-pharmacological SRs better discussed heterogeneity compared to pharmacological (AOR: 0.27, 95% CI: 0.09-0.85) or mixed interventions (AOR: 0.12, 95% CI: 0.03-0.53).
Conclusion: The methodological quality of gastric cancer intervention SRs is unsatisfactory. Future SRs should focus on establishing protocols, explaining study design selection, using comprehensive search strategies, documenting excluded studies with reasons, and describing primary studies in detail.