Table 1 Results of quality assessment using the Newcastle-Ottawa quality assessment scale

Selection

Comparability

Exposure

Study/item

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

Comparability of cohorts on the basis of the design or analysis

Assessment of outcome

Was follow-up long enough for outcomes to occur

Adequacy of follow up of cohorts

total