Results for NOS scale risk of bias assessment and Level of Evidence (OCEBM)
| Study | Selection | Comparability | Outcome | NOS score | OCEBM | ||||||
| A | B | C | D | E | F | G | H | I | |||
| McIntosh and McCrory34 | * | * | * | * | * | * | * | * | * | 9 | 3 |
| Marshall et al 30 | * | * | * | * | * | * | * | * | 8 | 3 | |
| Delaney et al 39 | * | * | * | * | * | * | 6 | 3 | |||
| Hollis et al 33 | * | * | * | * | * | * | * | * | * | 9 | 3 |
| Chalmers et al 29 | * | * | * | * | * | * | * | * | 8 | 3 | |
| Archbold et al 21 | * | * | * | * | * | * | * | * | * | 9 | 3 |
*Criteria met.
A, representativeness of the exposed cohort; B, selection of the non- exposed cohort; C, ascertainment of exposure; D, outcome of interest was not present at start of study; E, study controls for age, sex, injury history; F, study controls for additional factors; G, assessment of outcome; H, follow-up up long enough; I, adequacy of follow-up of cohorts; NOS, Newcastle-Ottawa Scale; OCEBM, Oxford Centre for Evidence-Based Medicine.