Fig. 1.

Flow chart of the article selection process. ^* Subgroup 1: Its principal objective was to describe, compare, evaluate, validate or develop a bias-control strategy for a known bias or limitation. ^† Subgroup 2: Estimated a measurement or identified risk factors for a disease, with the existence of bias being mentioned as a limitation of the study, regardless of whether or not strategies for its control were used. ^‡ Subgroup 3: Had characteristics different from those indicated above or was a conference paper with no abstract/full-text available