Table 8

Factors determining the quality of evidence according to GRADE

1. Risk of biasNot serious
  • Only two studies included in meta-analysis and both of them evaluated as unclear risk of bias

  • No serious limitations to downgrade the quality of evidence

  • Sequence generation was not reported in one study; allocation concealment not specified in both studies; no strategy reported to address issue of outcome assessor unblinding

  • Incomplete outcome data evaluated as ‘unclear’ in the pilot study; no mention of missing data or methods used to address missing data; no primary outcome stated for the pilot study

2. InconsistencyNot serious
  • I²=50%, which may be evaluated as either low or substantial heterogeneity; this overlap affects the decision making

  • Magnitude of heterogeneity could be the result of high variability in the sample size and effect size which justifies the decision

3. IndirectnessNot serious
  • Direct applicability of the included studies aims and objectives to their target populations, interventions and outcomes of interest

4. ImprecisionSerious
  • Boundaries of CI crossing the no effect line which downgrades the quality of evidence by one level

  • Number of participants needed for a single powered trial is higher than number of participants estimated from the meta-analysis; quality of evidence not downgraded on this basis

5. Publication biasUndetected
  • Selective outcome reporting domain evaluated low in both studies; publication bias considered as not serious by two reviewers