Table 4 Results of risk of bias assessment using the Newcastle-Ottawa risk of bias tool for cohort studies

Selection

Representativeness of the exposed cohort

–

–

*

–

–

–

*

*

Selection of the non-exposed cohort

*

*

*

*

*

*

*

*

Ascertainment of the exposure

*

*

*

–

*

–

–

*

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

*

*

*

–

*

*

–

–

Comparability

Comparability of cohorts on the basis of the design or analysis

Outcome

Assessment of outcome

*

*

*

–

*

–

–

*

Was follow-up long enough for outcomes to occur

–

–

*

*

*

*

–

–

Adequacy of follow-up cohorts

–

–

*

–

–

–

–

–