Table 3

The STOX classification system

Evidence typeSTOX classificationHealth Evidence Bulletins Wales classification33Description
Systematic reviewsS1IComprehensive systematic review containing at least one randomised controlled trial
S2IVComprehensive systematic review
TrialsT1IIRandomised controlled trial
T2IIINon randomised controlled trial
T3IIIBefore and after interventional trial
Observational studiesO1IVCohort study
O2IVCase-control study
O3IVCross sectional/longitudinal study (including statistical data)
O4IVStudy using qualitative methods only
O5IVCase study (for example, a single housing estate)
EXpressions of opinionXVFormal consensus or other professional opinion. (This category includes literature reviews where there is no indication of a systematic approach and models based on reviews of the literature)