Table 2.

Quality assessment of included studies based on the modified Newcastle-Ottawa scoring system (summarised from additional file 3, document 1)

Key for modified Newcastle-Ottawa domains:

Selection:

1. Representativeness of the exposed cohort

2. Selection of the non-exposed cohort

3. Ascertainment of exposure

4. Demonstration that the outcome of interest was not present at the start of the study

Comparability:

5. Comparability of cohorts based on design or analysis.

Outcome:

6. Assessment of outcome

7. Was follow-up long enough for outcomes to occur.

8. Adequacy of follow up of cohorts

Red = Failed to satisify domain (Reduces quality)

Amber = Moderately satisfied domain (moderately affects quality)

Green = Satisfied domain (Increases quality)