Guidelines and best practices emphasize the importance of blinding to mitigate potential biases in clinical studies. 1 Randomized controlled trials are considered the be the highest form of evidence and typically the goal has been to conduct a placebo controlled double-blinded trial. 2 Risk of bias (RoB) assessment is a crucial part of evidence synthesis. 3 Typically, this evaluation is carried out using tools such as Cochrane's original RoB tool and the revised RoB 2.0 tool. 4,5 The original RoB tool explicitly assesses blinding through separate domains for blinding of participants and personnel (performance bias), as well as blinding of outcome assessment (detection bias). 4 In RoB 2.0, blinding assessment is part of the measurement of the outcome domain. 5 However, both tools consider blinding within the context of the outcome's nature, whether it is objective for the patient, treating personnel, the outcome assessor, all of these, or none.The objectivity of the outcome plays a pivotal role in assessing bias risk when evaluating blinding, especially concerning subjective outcomes where the absence of blinding could significantly affect effect sizes. 6 Previous meta-epidemiological studies have mostly reported that the blinding has influence only on subjective outcomes. 6,7 Interestingly, one of the latest and largest meta-epidemiological studies did not find evidence that blinding would even have an influence on subjective outcomes neither. 8 Thus, it is plausible to assume that the effect of blinding on objective outcomes is either negligible or even nonexistent in medicine.A key part of the evidence synthesis is to appraise the evidence certainty. The most widely used method is to assess the evidence certainty according to the Grading and Recommendations (GRADE). 9 GRADE rates each outcome according to different domains, of which one is risk of bias. 10 Thus, to make an accurate judgment on evidence certainty, risk of bias in studies should be adequately assessed. A previous meta-epidemiological study of neonatal meta-analyses showed evidence certainties were often downgraded due to lack of blinding even in the objective outcomes. 11 Thus, inadequate downgrading of evidence certainty may have direct influence to treatment guidelines and patient care. 12 The aim of this study was to investigate how the authors of systematic reviews and meta-analyses published in top level journals and Cochrane have estimated the risk of bias due to blinding and have they noted the objectivity of the outcomes in their assessments.