The quality assessment in cohort studies
| Study items | Zhang et al23 | Wang and Jin24 | Guo et al25 | Liu and Zhu26 | |
| Selection | Representativeness of the exposed cohort | 1 | 1 | 1 | 1 |
| Selection of the non-exposed cohort | 1 | 1 | 1 | 1 | |
| Ascertainment of exposure | 1 | 1 | 1 | 1 | |
| Demonstration that outcome of interest was not present at start of study | 1 | 1 | 1 | 1 | |
| Comparability | Comparability of cohorts on the basis of the design or analysis | 2 | 1 | 1 | 1 |
| Outcome | Assessment of outcome | 1 | 1 | 1 | 1 |
| Was follow-up long enough for outcomes to occur | 1 | 1 | 1 | 0 | |
| Adequacy of follow-up of cohorts | 0 | 1 | 1 | 1 | |
| NOS score | 8 | 8 | 8 | 7 | |
NOS, Newcastle-Ottawa Scale.