Data analysis

Descriptive variables including bibliographic characteristics and methodological quality were reported as frequencies with percentages and medians with ranges, as appropriate. The Kruskal-Wallis rank test was applied to evaluate the differences in overall methodological quality across SRs with varied bibliographic features.

Based on findings from previous methodological research [13–15], seven bibliographic characteristics of SRs were selected as independent variables in regression analyses to investigate their potential association to the rigor of SRs, including (i) whether the SR was a Cochrane SR; (ii) whether the SR was an update of a previous SR; (iii) types of treatment; (iv) publication year; (v) publication journal impact factor in the year before SR publication; (vi) number of authors in the SR; and (vii) location of the corresponding author. To examine potential associations between overall methodological quality and bibliographic characteristics, multi-ordinal regressions were conducted. Associations between ratings of individual AMSTAR2 items and bibliographic characteristics were further examined using either binary logistic regression (for items 1, 3, 5, 6, and 10–16) or multinomial logistic regression (items 2, 4, and 7–9). In multi-ordinal regression analysis, binary logistic regression analysis, and multinomial logistic regression analysis, the model fit was evaluated using the Pearson/deviance test, Hosmer-Lemeshow test, and likelihood ratio test. Adjusted odds ratios (AORs) and 95% confidence intervals (CIs) were calculated to quantify the associations between AMSTAR2 ratings and bibliographic characteristics. A p <0.05 indicated statistical significance. Data analyses were conducted by IBM SPSS v26.