Table 2 Risk of bias in individual studies
Study | Study participation | Study attrition | Risk factor measurementa | Outcome measurement | Study confounding | Statistical analysis and reporting |
|---|---|---|---|---|---|---|
Akiyama [48] | Low risk | High risk | Moderate risk | Low risk | High risk | High risk |
Cao [49] | Low risk | High risk | Moderate risk | Low risk | Moderate risk | Moderate risk |
Hozumi [51] | Low risk | High risk | Moderate risk | Low risk | Moderate risk | Moderate risk |
Ishikawa [53] | Moderate risk | Low risk | Low risk | Low risk | High risk | High risk |
Liang [54] | Low risk | Low risk | High risk | Low risk | High risk | Low risk |
Manfredi [55] | Low risk | High risk | Moderate risk | Low risk | High risk | High risk |
Okamoto [56] | High risk | Low risk | High risk | Low risk | High risk | High risk |
Silva [59] | Moderate risk | Low risk | Low risk | Low risk | High risk | High risk |
Singh [60] | Low risk | Low risk | Low risk | Low risk | Moderate risk | High risk |
Su [61] | Moderate risk | Low risk | Low risk | Low risk | High risk | High risk |
Suda [62] | Low risk | High risk | Moderate risk | Low risk | High risk | High risk |
Yamakawa [64] | Moderate risk | High risk | Low risk | Low risk | Moderate risk | High risk |
Study | Study participation | Study attrition | Prognostic factor measurementa | Outcome measurement | Study confounding | Statistical analysis and reporting |
Cao [49] | Low risk | High risk | Moderate risk | Low risk | Moderate risk | Moderate risk |
Enomoto [50] | Moderate risk | High risk | Moderate risk | Low risk | High risk | Moderate risk |
Ichiyasu [52] | High risk | High risk | Low risk | Low risk | High risk | High risk |
Liang [54] | Low risk | Low risk | Moderate risk | Low risk | Moderate risk | Low risk |
Manfredi [55] | Low risk | High risk | Moderate risk | Low risk | High risk | High risk |
Ota [57] | Low risk | Low risk | Moderate risk | Low risk | Moderate risk | High risk |
Parambil [58] | Low risk | Low risk | High risk | Low risk | High risk | High risk |
Silva [59] | Moderate risk | Low risk | Low risk | Low risk | High risk | High risk |
Singh [60] | Low risk | Low risk | Low risk | Low risk | Moderate risk | High risk |
Toyoda [63] | Low risk | High risk | High risk | Low risk | High risk | High risk |