Table 2 The methodological quality assessment of the observational studies

Representative of the exposed cohort

*

*

*

*

Selection of the external control

*

*

*

*

Ascertainment of exposure

x

x

x

x

Outcome of interest not present at the start of the study

*

*

*

*

Comparability

Main factor and additional factor based on comparability of cohorts

*

*

*

*

Outcome

Assessment of outcomes

*

*

*

*

Sufficient follow up time

*

*

*

*

Adequacy of follow up

*

*

*

*