Quality assessment of included cohort studies based on the Newcastle-Ottawa scale.

*a maximum of 1 point for each item
**a maximum of 2 points for each item
***a maximum of 1 point for each item
****a maximum of 9 points
1 a) truly representative of the average individuals in the community *, b) somewhat representative of the average individuals in the community *, c) selected group of users, d) no description of the derivation of cohort
2 a) drawn from the same community as the exposed group *, b) drawn from a different source, c) no description of the derivation of the non-exposed-group
3 a) secure record *, b) structured interview or questionnaire *, c) written self reports, d) no description
4 a) yes *, b) no
5 a) study control for one confounding variable *, b) study control for 2 or more confounding variables **
6 a) independent blind assessment *, b) record linkage *, c) self reports d) no description
7 a) yes (select an adequate follow up period for outcome of interest *, b) no
8 a) complete follow up—all subjects accounted for *, b) subjects lost to follow up are unlikely to introduce bias—≤20% loss or ≥80% follow up, or description provided of those lost *, c) ≥20% loss or ≤80% follow up, or no description of those lost, d) no statement
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