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Updated: Dec 27, 2025

A Clinical Trial Assessing the Safety, Efficacy, and Delivery of Olive-Oil-Based Three-Chamber Bags for Parenteral Nutrition
Published on: September 20, 2019
[Risk of bias in controlled clinical trials]
C Schmucker1, J J Meerpohl2, A Blümle2
1Institut für Evidenz in der Medizin (für Cochrane Deutschland Stiftung), Medizinische Fakultät, vertreten durch das Universitätsklinikum Freiburg, Albert-Ludwigs-Universität, Breisacher Str. 153, 79110, Freiburg, Deutschland. schmucker@ifem.uni-freiburg.de.
Abstract:
Results from clinical studies are often subject to the risk of bias (deviation from the truth, systematic error). Therefore, a critical appraisal of studies provides a useful strategy in evidence-based healthcare to safeguard against wrong decisions and resulting in overtreatment or undertreatment. This article explains the frequently encountered types of bias, differentiates between them and provides strategies for avoidance of systematic errors. In addition, the two established Cochrane tools with which the risk of bias can be assessed in randomized and non-randomized studies are presented. To highlight the most important components of these tools for bias assessment, examples of randomization, confounding, blinding, completeness of data and selective reporting are provided. Finally, it is shown that bias should not be confused with other study limitations, such as external validity and imprecision.
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