Level 4 Evidence: Clinical Case Series
Studies are assessed by the level of evidence presented in their findings and the effects that variable biases may inflict upon the overall validity of the study’s findings; case series represent a Level IV study. Case series are “descriptive,” observational studies that describe general disease characteristics. Case series do not test a hypothesis or make use of a comparison group to determine the efficacy of a treatment; they follow a group of patients over a period of time who have a similar diagnosis or are being treated with the same procedure. Case series aid in analysis of unusual occurrences of a disease. Case series exclusively report the outcomes following a novel treatment procedure for a specific study population and are presented only by descriptive statistics. The variable potential for bias is important to explicitly state for future prospective studies to ascertain validity of the treatment and for future comparisons of outcomes relative to physical function and well-being, most often deemed significant by measures of validity and reliability. In the instance of unusual occurrences of a disease, case series are highly effective for designing hypotheses for future prospective studies, although no hypothesis is tested within the case series itself.
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