Table 1 Examples of types of empirical studies for which tools to assess methodological limitations are already available

• Randomized studies such as randomized trials and cluster randomized trials

• Quasi-experimental (non-randomized) and observational studies such as ITS, CBAs, cohort studies, case–control studies and regression analyses

• Economic evaluations

• Primary qualitative studies

• Systematic reviews of the effectiveness of interventions

• Qualitative evidence syntheses/systematic reviews of qualitative evidence