Results: Large differences between studies were found, with significant heterogeneity in epidemiological indicators.

Sensitivity analysis and random-effects model were performed for assessing significant heterogeneity.

There was no significant heterogeneity among studies for subgroup analysis.

There was no significant heterogeneity across all included studies for the measurements we evaluated.

There was significant heterogeneity between studies for both HR estimates.

Fentanyl doses added no significant heterogeneity as shown by meta-regression.

There was no statistically significant heterogeneity in SNP or haplotype odds ratios across cohorts.

Due to significant heterogeneity, subgroup and meta-regression analyses were undertaken.

There was significant heterogeneity in antifungal medication selection and duration.

There was no significant heterogeneity in COX-2 protein expression.

Several single arm prospective and retrospective reports were also identified with significant heterogeneity and often-contradictory conclusions.

Clinical isolates of Mycobacterium tuberculosis demonstrate significant heterogeneity in virulence potential in animal models of infection.

However, there was significant heterogeneity of the results.

Concerning postoperative complications, there were no significant differences between the two groups with no significant heterogeneity.

We performed fixed effect meta-analysis except where significant heterogeneity called for use of a random effects analysis.

The certainty of evidence was low to moderate: the main limitations were imprecision and statistically significant heterogeneity.