1.4 Quality assessment
We used the Newcastle-Ottawa Scale (NOS) to assess the quality of each
cohort and case-control studies 44. It evaluated the
quality of articles from case and control selection, exposure record,
the comparability and the outcome. The average score of quality
assessment was 8.1 of the cohort studies and 8.0 of the case-control
studies. The lowest was 7 and the highest was 9. (Table S3- S4)