Table 1 Overview of quality domains

Study participation

The study sample represents the population of interest on key characteristics, sufficient to limit potential bias of the extracted results

Source population clearly defined. Study population described (inclusion and exclusion criteria). Study population represents population of interest.

Study attrition

Loss to follow-up (from target population to final study sample) is not associated with key characteristics (i.e. the study sample adequately represents the population of interest). This is sufficient to limit bias of the extracted results.

Completeness and transparency of follow-up described for each relevant point of follow-up. Completeness of follow-up adequate. Reasons for loss to follow-up are adequately described for key characteristics.There are no important differences between key characteristics and outcomes in participants who completed the study and those who did not.

Prognostic factor measurement

The prognostic factors of interest are adequately measured in study participants to sufficiently limit bias of the extracted results

Prognostic tests are defined well enough to be replicated. The performance of the prognostic tests are standardized appropriately.

Outcome measurement

The outcome of interest is adequately measured in study participants to sufficiently limit bias of the extracted results.

Outcomes are defined. Outcome measures are well established. Method, setting and time of outcome measurements are the same for all participants.

Analysis & reporting

The statistical analysis and reporting of results is transparent and appropriate in relation to the study, limiting potential for presentation of invalid results

There is sufficient presentation of data to assess the adequacy of the analysis.The statistical analysis is sufficiently described and appears appropriate in relation to the part of the study that concerns the present review. There is no selective reporting of results.