Table 2 The Newcastle–Ottawa Scale(NOS) scores of the studies included in the meta-analysis

Selection

Comparability

Outcome

Study

Representativeness of the exposed cohort

Selection of the non-exposed cohort

Ascertainment of exposure

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

Control for important factors ^a

Assessment of outcome

Was follow-up long enough for outcomes to occur

Adequacy of follow-up of cohorts

Scores