Concerns about the Burden of Proof studies

We read with interest the Burden of Proof (BoP) studies 1 , 2 , 3 , 4 , 5 in which the authors conducted meta-analyses of epidemiological studies to provide an overall conservative quantitative assessment for several important public health questions. For ease of interpretation, they transformed the overall assessment into a star rating (1–5 stars). Examples include five stars for smoking and lung cancer, two stars for low vegetable intake and ischemic heart disease (IHD) and two stars for unprocessed red meat and type 2 diabetes (T2D), colorectal cancer and IHD 6 . They used this same method to assign just three stars to smoking in relation to IHD and one or two stars to other well-established relationships 1 , 2 , 3 , 4 . However, we believe there are serious methodological issues with their meta-analyses 5 ; the star rating of evidence strength is overly simplistic and could cast doubt on existing recommendations and policies intended to prevent chronic disease and treat illnesses.