Table 1 Results of quality assessment of studies using the QUIPS tool
Study | Study participation | Study attrition | Prognostic factor measurement | Outcome measurement | Study confounding | Statistical analysis and reporting | Overall risk of bias |
|---|---|---|---|---|---|---|---|
Foster et al. 1989 [42] | High | Moderate | High | High | Moderate | High | High |
Elliott et al. 1992 [54] | Moderate | Low | High | High | Moderate | High | High |
Hardcastle et al. 1992 [55] | Moderate | Low | High | High | High | High | High |
Elliott et al. 1993 [56] | Moderate | Low | High | Moderate | Moderate | Moderate | High |
Burnett et al. 1996 [43] | Moderate | High | High | High | High | Moderate | High |
Elliott & Khangure 2002 [65] | Moderate | High | High | Moderate | High | Moderate | High |
Portus et al. 2004 [60] | Moderate | Moderate | High | Moderate | High | Moderate | High |
Engstrom et al. 2007 [44] | Moderate | Low | High | Moderate | Low | Low | High |
Stuelcken et al. 2008 [57] | High | Low | Low | Moderate | Low | Moderate | High |
Ranson et al. 2010 [45] | High | Moderate | Low | Low | High | Moderate | High |
Stuelcken et al. 2010 [58] | High | Low | Moderate | Moderate | High | Low | High |
Kountouris et al. 2012 [46] | Moderate | Moderate | High | Low | Low | Moderate | High |
Kountouris et al. 2013 [47] | High | Moderate | High | Low | Low | Moderate | High |
Olivier et al. 2014 [48] | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | High |
Gray et al. 2016 [62] | Moderate | Low | Low | Low | High | Moderate | High |
Bayne et al. 2016 [49] | Moderate | High | Low | High | Low | High | High |
Olivier et al. 2017 [50] | Moderate | Moderate | Moderate | Low | High | Low | High |
Alway et al. 2019 [51] | Moderate | Low | Low | Low | Moderate | Low | Moderate |
Alway et al. 2019 [63] | Moderate | Low | Moderate | Moderate | Moderate | Low | Moderate |
Kountouris et al. 2019 [52] | Moderate | Low | Moderate | Low | Moderate | Low | High |
Senington et al. 2020 [61] | High | Moderate | Moderate | Moderate | High | Low | High |
Alway et al. 2021 [53] | Moderate | Moderate | High | High | High | Low | High |
Taylor et al. 2021 [64] | High | Low | High | Low | Moderate | High | High |
Sims et al. 2021 [59] | Moderate | Low | High | Low | Low | Low | High |
Keylock et al. 2022 [41] | Moderate | High | Low | High | Low | Low | High |