Table 2

Assessment of study quality

StudyStudy designNewcastle Ottawa scoringScore (9)Risk of bias
Selection (4)Comparator (2)Outcome (3)
Cothren et al22Retrospective cohort****4High
Snow et al13Retrospective cohort*****5High
Biffl et al24Retrospective cohort****4High
Wei et al11Retrospective cohort****4High
Miller et al6Retrospective cohort****4High
Stein et al19Retrospective cohort*******7Moderate
Cothren et al21Prospective cohort*****5Moderate
Malhotra et al20Prospective cohort*****5High
Wagenaar et al10Retrospective cohort*******7Moderate
Callcut et al16Retrospective cohort********8Low
Burlew et al14Retrospective cohort***3High
DiCocco et al17Retrospective cohort*******7Moderate
Miller et al23Prospective cohort*****5High
Biffl et al2Retrospective cohort*****5High
Cothren9Retrospective cohort******6Moderate
Biffl et al7Retrospective cohort*****5Moderate
Lebl et al15Retrospective cohort*****5High
Hwang et al18Retrospective cohort*****5High
Catapano et al5Retrospective cohort******6Moderate
  • Low risk of bias: 3 or 4 stars in selection domain and 1 or 2 stars in comparability domain and 2 or 3 stars in outcome/exposure domain.

  • Moderate risk of bias: 2 stars in selection domain and 0, 1, or 2 stars in comparability domain and 2 or 3 stars in outcome/exposure domain (modified to reflect the often appropriate omission of regression based on number of outcomes).

  • High risk of bias: 0 or 1 star in selection domain or 0 star in comparability domain or 0 or 1 star in outcome/exposure domain.