Newcastle–Ottowa Scale (NOS) quality assessment tool
| Study | Domains of point loss in NOS scale | Score out of 7 |
| Cohort studies | ||
| Hnizdo and Sluis-Cremer, 199319 | Exposure measure | 6 |
| Steenland and Brown, 199514 | – | 7 |
| Hughes et al, 199822 | – | 7 |
| Chen et al, 200510 | Exposure measure, lack of outcome at onset | 5 |
| Liu et al, 201325 | Exposure measure, lack of outcome at onset | 5 |
| Cross-sectional studies | ||
| Kreiss and Zhen, 199618 | – | 7 |
| Rosenman, 199623 | Non-respondents/comparability | 6 |
| Miller et al, 199811 | – | 7 |
Criteria are described in greater detail in online supplemental file 2 and 4.