Table 2.
Newcastle–Ottawa Scale for quality assessment of nonrandomized studies
| Study | Design | Selection | Comparability | Outcome | Total Points | ||||||
| S1 | S2 | S3 | S4 | C1 | C2 | O1 | O2 | O3 | |||
| Friend et al. (15) | Retrospective cohort | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 8 |
| Rasgon et al. (16) | Prospective cohort | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 5 |
| Wingard et al. (17) | Prospective cohort | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 8 |
| Souqiyyeh et al. (18) | Retrospective cohort | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 3 |
| Hanko et al. (19) | Retrospective cohort | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Lacson et al. (20) | Prospective cohort | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 8 |
| Ghaffari (21) | Prospective cohort | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 6 |
| Wilson et al. (22) | Retrospective cohort | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 8 |
| Yu et al. (23) | Retrospective cohort | 1 | 1 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 4 |
| Gill et al. (24) | Retrospective cohort | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 9 |
| Schanz et al. (25) | Retrospective cohort | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 6 |
For quality assessment, >7 points is considered “high quality.” S1, representativeness of exposed cohort; S2, selection of controls; S3, ascertainment of exposure; S4, outcome not present at start of study; C1/C2, design/analysis controls for important factors; O1, assessment of outcomes; O2, follow-up duration sufficient for outcomes to occur; O3, all subjects accounted for.