First author [ref.] | Study participation | Study attrition | Prognostic factor measurement | Outcome measurement | Study confounding | Statistical analysis reporting |
Holverda [21] | Low | Moderate | Low | Low | Moderate | Low |
Boerrigter [18] | Low | Low | Low | Low | Moderate | Low |
Thirapatarapong [11] | Low | Moderate | Low | Low | High | Low |
Adir [12] | Low | Low | Moderate | Low | High | Moderate |
Skjørten [28] | Low | Low | Low | Low | Low | Low |
Xiong [29] | Low | Low | Low | Low | Moderate | Low |
Blanco [10] | Low | Moderate | Moderate | Low | Moderate | Low |