Table 2 Quality assessment approaches

Canivano and Gracia [10]

None

N/A

N/A

HTA report [8]

Quality assessment tool derived from QUADAS [19] and the Hayden checklist relating to prognostic studies [20]

Results of the quality assessment were presented

Impact commented on but sensitivity analyses not deemed possible.

Krasopoulos et al. [11]

Study eligibility criterion: investigators to be blinded to patients’ aspirin status

Quality rating for risk of bias (A to D) but not explicit on how this was derived

No

Terminology used was confusing (e.g. ‘allocation of blindness’ and ‘compliance with blindness’). The term ‘allocation concealment’ used in the context of observational studies is not appropriate

Li et al. [15]

Study eligibility criterion: only those studies with verified compliance. Newcastle-Ottawa checklist [21] for cohort studies

Findings presented

No

Pusch et al. [12]

None

N/A

N/A

Sofi et al. [14]

Study eligibility criterion: prospective study design

N/A

N/A

Snoep et al. [13]

Quality criteria relating to: control for confounders, measurement of exposure, completeness of follow-up and blinding, and, for case–control studies, matching and case definition

No

No

Wisman et al. [16]

Modified QUADAS tool [19] (for quality assessment of diagnostic accuracy studies). 11 items assessed

Findings presented

Sensitivity analysis. Studies scoring ‘low risk of bias’ on eight or more of the quality items were considered to be good quality