Table 4 Possible responses to individual items in modified Graphical Appraisal Tool for Epidemiological studies (GATE)

++

Indicates that for that particular aspect of study design, the study has been designed or conducted in such a way as to minimise the risk of bias.

+

Indicates that either the answer to the checklist question is not clear from the way the study is reported, or that the study may not have addressed all potential sources of bias for that particular aspect of study design.

-

Should be reserved for those aspects of the study design in which significant sources of bias may persist.

Not reported (NR)

Should be reserved for those aspects in which the study under review fails to report how they have (or might have) been considered.

Not applicable (NA)

Should be reserved for those study design aspects that are not applicable given the study design under review (for example, allocation concealment would not be applicable for case control studies).