Table 1 Quality assessment criteria
From: Systematic review of effect of community-level interventions to reduce maternal mortality
High quality | Medium quality | Low quality | |
|---|---|---|---|
1. Selection bias: | Studies with randomisation, allocation concealment, similarity of groups at baseline | RCTs with some deficiencies in randomisation e.g. lack of allocation concealment, or non-randomised studies with either similarities at baseline or use of statistical methods to adjust for any baseline differences | Non randomised, with obvious differences at baseline, and without analytical adjustment for these differences. |
2. Performance bias:* | Differed only in intervention, which was adhered to without contamination, groups were similar for co-interventions or statistical adjustment was made for any differences | Confounding was possible but some adjustment was made in the analysis | Intervention was not easily ascertained or groups were treated unequally other than for intervention or there was non-adherence, contamination or dissimilarities in groups and no adjustments made. |
3. Measurement bias: | Outcome measured equally in both groups, with adequate length of follow-up (i.e. at least 6 weeks postpartum), direct verification of outcome, with data to allow calculation of precision estimates. | Inadequate length of follow up or length not given | Inadequate reporting or verification of maternal mortality or differences in measurement in both groups |
4. Attrition bias: | No systematic differences in withdrawals between groups and with appropriate imputation for missing values | Incomplete follow-up data, not intention-to-treat analysis or lacking reporting on attrition |