Table 2.
The risk of bias for the included studies (Newcastle-Ottawa scale)
| Study | Selection | Comparability | Outcome | Total | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| REC | SNEC | AE | DO | SC | AF | AO | FU | AFU | ||
| Laurent [24] | 1 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 6 |
| Yamamoto [25] | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 8 |
| Park [26] | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| Chi [18] | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| Fujimoto [28] | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 1 | 6 |
REC representativeness of the exposed cohort, SNEC selection of the non-exposed cohort, AE ascertainment of exposure, DO demonstration that outcome of interest was not present at start of study, SC study controls for age and sex, AF study controls for any additional factors (chemoradiotherapy, curative resection), AO assessment of outcome, FU follow-up long enough for outcomes to occur, AFU adequacy of follow-up of cohorts