Hierarchy of Evidence Within the Medical Literature

Abstract

The quality of evidence from medical research is partially deemed by the hierarchy of study designs. On the lowest level, the hierarchy of study designs begins with animal and translational studies and expert opinion, and then ascends to descriptive case reports or case series, followed by analytic observational designs such as cohort studies, then randomized controlled trials, and finally systematic reviews and meta-analyses as the highest quality evidence. This hierarchy of evidence in the medical literature is a foundational concept for pediatric hospitalists, given its relevance to key steps of evidence-based practice, including efficient literature searches and prioritization of the highest-quality designs for critical appraisal, to address clinical questions. Consideration of the hierarchy of evidence can also aid researchers in designing new studies by helping them determine the next level of evidence needed to improve upon the quality of currently available evidence. Although the concept of the hierarchy of evidence should be taken into consideration for clinical and research purposes, it is important to put this into context of individual study limitations through meticulous critical appraisal of individual articles.

Case series: raw, whole, plant-based nutrition protocol rapidly reverses symptoms in three women with systemic lupus erythematosus and Sjögren’s syndrome

“…In the hierarchy of evidence, case series provide weak evidence for causality on their own and best serve to provoke consideration for future research. Case series are, however, important for sharing experiences between clinicians and generating hypotheses that may lead to future research ( 63 ). As this is a case series, we cannot conclude whether the dietary change alone was responsible for the observed improvement in symptoms; it is not possible to assess confounding factors that may be responsible for the improvement.…”

Time to Load Up–Resistance Training Can Improve the Health of Women with Polycystic Ovary Syndrome (PCOS): A Scoping Review

“…The greatest number of statistical findings presented in this scoping review come from a case–control study [ 48 ] where the data has repeatedly been analysed to address multiple hypotheses. Whilst Lara and colleagues have the largest sample of women with PCOS completing an intervention, there are inherent limitations with this study design (e.g., risk of selection bias) that reduce our confidence in the certainty of the findings [ 52 ].…”

The use of Qigong and Tai Chi in the management of temporomandibular joint dysfunction: A systematic review

“…The methodology of this systematic review was reported based on guidelines in the Preferred Reporting Items for Systematic Reviews and Meta-analysis checklist. 22,24 The AMSTAR 2 checklist also informed the conduct of the review's methodological processes. 25 with the aid of "OR" and "AND" Boolean operators, using different search terms on Tai Chi, Qigong, and TMJ.…”