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Levels of evidence (LOE) are classification systems that use a hierarchal structure to indicate where the research in question may fall in regard to the strength of the recommendations. They have been used in some form in medical literature since the 1970s and have continued to be refined for ease of use by the practicing physician.
The purpose of this article is to define LOE as commonly used in the orthopaedic literature and to highlight that LOE alone is not always sufficient for assessing the quality of the evidence presented. Examples of research at different LOE are presented and discussed, highlighting the importance of critical appraisal when using these guidelines.