Table 2. Newcastle-Ottawa quality assessment form for case-control study and cohort study.
| Variable | Selection | Comparability | Outcome/Exposure | Total score | Quality power | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| For case-control study | Adequate definition of case | Representativeness of case | Selection of control | Definition of control | Comparability of cases and controls on the basis of the design or analysis | Ascertainment of exposure | Same method of ascertainment for cases and controls | Non response rate | ||
| Irwig (2012) [9] | ★ | ★ | ★ | ★ | ★ | ★★★★★ (5) | Poor | |||
| Pietrzyk et al (2015) [14] | ★ | ★ | ★ | ★★ | ★ | ★ | ★★★★★★★ (7) | Good | ||
| For cohort study | Representativeness of the exposed cohort | Selection of the non-exposed cohort | Ascertainment of exposure | Outcome of interest not present at start of study | Comparability of cohorts on the basis of the design or analysis | Ascertainment of outcome | Adequacy of duration of follow-up | Adequacy of completeness of follow-up | ||
| Unger et al (2016) [15] | ★ | ★ | ★ | ★ | ★★ | ★ | ★ | ★★★★★★★★ (8) | Good | |
| Welk et al (2017) [16] | ★ | ★ | ★ | ★ | ★★ | ★ | ★ | ★★★★★★★★ (8) | Good | |
| Hagberg et al (2017) [20] | ★ | ★ | ★ | ★ | ★★ | ★ | ★ | ★★★★★★★★ (8) | Good | |
A study can be awarded a maximum of one star for each numbered item except for Comparability. A maximum of two stars can be awarded for Comparablitily. Good quality, 3 or 4 stars in selection domain AND 1 or 2 stars in comparability domain AND 2 or 3 stars in oucome/exposure domain. Fair quality, 2 stars in selection domain AND 1 or 2 stars in comparability domain AND 2 or 3 stars in oucome/exposure domain. Poor quality, 0 or 1 star in selection domain OR 0 stars in comparability domain OR 0 or 1 stars in oucome/exposure domain.