Table 2 Results of quality assessment using the Newcastle–Ottawa Scale(NOS) for cohort studies

Selection

Comparability

Outcome

Study

Representativeness of exposed cohort

Selection of non-exposed cohort

Ascertainment of exposure

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

Comparability of Cohorts on the basis of the design or analysis

Assessment of outcome

Follow-up long enough for outcomes

Adequacy of follow up

Quality

score