Table 3. The assessment of the risk of bias in each enrolled study using the newcastle–Ottawa scale (NOS).
| Study [ref] | Selection (0–4) | Comparability (0–2) | Outcome (0–3) | Total scale (NOS) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| REC | SNEC | AE | DO | SC | AF | AO | FU | AFU | ||
| Costa C [11] | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 7 |
| Ristimaki A [12] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Denkert C [13] | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 8 |
| Spizzo G [14] | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 8 |
| Wulfing P [15] | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 7 |
| John K [16] | 1 | 0 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Surowiak P [17] | 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 8 |
| Gunnarsson C [18] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Park K [19] | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 0 | 1 | 7 |
| Narssar A [20] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Zerkowski MP [21] | 1 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 8 |
| Zhang XH [22] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Glynn SA [23] | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Miglietta A [24] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Rozenowicz RD [25] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Barisik NO [26] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Ciris IM [27] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Holmes MD [28] | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | 8 |
| Sondes KC [29] | 1 | 0 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 7 |
| Dhakal HP [30] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 5 |
| Kargi A [31] | 1 | 1 | 1 | 0 | 1 | 1 | 0 | 0 | 1 | 6 |
REC: representativeness of the exposed cohort; SNEC: selection of the nonexposed cohort; AE: ascertainment of exposure; DO: demonstration that outcome of interest was not present at start of study; SC: study controls for age, sex; AF: study controls for any additional factors (chemoradiotherapy, curative resection); AO: assessment of outcome; FU: follow-up long enough (36 Months) for outcomes to occur; AFU: adequacy of follow-up of cohorts (≥ 90%). “1” means that the study is satisfied the item and “0” means the opposite situation.