Table 4.

Definitions used by the BTF to describe the quality of a study used in the production of their guidelines and definition of ‘levels of recommendation’ which can be made, regarding the overall strength of a BTF guidance.

An individual study can be classed based on quality of its design and integrity of data.

Class 1: derived from good-quality RCTs with solid methodology and large patient numbers

Class 2: derived from cohort studies where comparison of two or more groups is clearly distinguished, or from flawed RCTs

Class 3: derived from case series, databases/registries, case reports, and expert opinion, flawed RCTs, cohort, or case-control studies

A body of evidence is used to formulate a guideline. The quality and strength of the body of evidence defines the level of recommendation given to each guideline.

Level I: a high-quality body of evidence. Two or more Class 1 studies

Level II A: a moderate-quality body of evidence. Class 1 studies with inconsistent results or class 2 studies

Level II B: a low-quality body of evidence consisting of Class 2 studies, with direct evidence but of overall low quality

Level III: a low-quality body of evidence consisting of Class 3 studies, or Class 2 studies providing only indirect evidence

Insufficient: no evidence identified or quality too poor to make a recommendation