Quality assessment for studies
| Newcastle-Ottawa Quality Assessment Scale for cohort studies18 | ||||||||||
| Study | Type of study | Selection | Comparability | Outcome | ||||||
| Representativeness of the exposed cohort | Selection of the non-exposed cohort | Ascertainment of exposure/risk factor, that is, severe versus non-severe | 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 score (out of 8 stars) | ||
| Huang et al 11 | Prospective cohort | * | * | * | 0 (No) | * | * | * | * | 7 stars |
| Zhang et al 8 | Retrospective cohort study | * | * | * | 0 (No) | * | * | Follow-up period not mentioned | Unable to assess | 5 stars |
| Wang et al 9 | Retrospective cohort study | * | * | * | * (Yes) | * | * | * | * | 8 stars |
| Pan et al 14 | Descriptive cross-sectional study with a prospective cohort component | * | * | * | * (Yes) | * | * | * | * | 8 stars |
| Guan et al 22 | Retrospective cohort study | * | * | * | * (Yes) | * | * | * | * | 8 stars |
*Indicates one star.