What type of evidence is based on data and derived from systematic study of one or more effectiveness criteria?

It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.

1Research Associate, Section of Plastic Surgery, Department of Surgery, The University of Michigan Health System

Find articles by Patricia B. Burns

Rod J. Rohrich

2Professor of Surgery, Department of Plastic Surgery, University of Texas Southwestern Medical Center

Find articles by Rod J. Rohrich

Kevin C. Chung

3Professor of Surgery, Section of Plastic Surgery, Department of Surgery, The University of Michigan Health System

Find articles by Kevin C. Chung

Disclaimer

1Research Associate, Section of Plastic Surgery, Department of Surgery, The University of Michigan Health System

2Professor of Surgery, Department of Plastic Surgery, University of Texas Southwestern Medical Center

3Professor of Surgery, Section of Plastic Surgery, Department of Surgery, The University of Michigan Health System

Corresponding Author: Kevin C. Chung, MD, MS, Section of Plastic Surgery, University of Michigan Health System, 2130 Taubman Center, SPC 5340, 1500 E. Medical Center Drive, Ann Arbor, MI, 48109-5340, ude.hcimu@gnuhccek, Phone 734-936-5885, Fax 734-763-5354

Copyright notice

The publisher's final edited version of this article is available at Plast Reconstr Surg

Abstract

As the name suggests, evidence-based medicine (EBM), is about finding evidence and using that evidence to make clinical decisions. A cornerstone of EBM is the hierarchical system of classifying evidence. This hierarchy is known as the levels of evidence. Physicians are encouraged to find the highest level of evidence to answer clinical questions. Several papers published in Plastic Surgery journals concerning EBM topics have touched on this subject.– Specifically, previous papers have discussed the lack of higher level evidence in PRS and need to improve the evidence published in the journal. Before that can be accomplished, it is important to understand the history behind the levels and how they should be interpreted. This paper will focus on the origin of levels of evidence, their relevance to the EBM movement and the implications for the field of plastic surgery as well as the everyday practice of plastic surgery.

Keywords: Evidence-based medicine, levels of evidence

History of Levels of Evidence

The levels of evidence were originally described in a report by the Canadian Task Force on the Periodic Health Examination in 1979. The report’s purpose was to develop recommendations on the periodic health exam and base those recommendations on evidence in the medical literature. The authors developed a system of rating evidence (Table 1) when determining the effectiveness of a particular intervention. The evidence was taken into account when grading recommendations. For example, a Grade A recommendation was given if there was good evidence to support a recommendation that a condition be included in the periodic health exam. The levels of evidence were further described and expanded by Sackett in an article on levels of evidence for antithrombotic agents in 1989 (Table 2). Both systems place randomized controlled trials (RCT) at the highest level and case series or expert opinions at the lowest level. The hierarchies rank studies according to the probability of bias. RCTs are given the highest level because they are designed to be unbiased and have less risk of systematic errors. For example, by randomly allocating subjects to two or more treatment groups, these types of studies also randomize confounding factors that may bias results. A case series or expert opinion is often biased by the author’s experience or opinions and there is no control of confounding factors.

Table 1

Canadian Task Force on the Periodic Health Examination’s Levels of Evidence*

LevelType of evidenceIAt least 1 RCT with proper randomizationII.1Well designed cohort or case-control studyII.2Time series comparisons or dramatic results from uncontrolled studiesIIIExpert opinions

Open in a separate window

*Adapted from Canadian Task Force on the Periodic Health Examination. The periodic health examination. Can Med Assoc J 1979;121:1193-254

Table 2

Levels of Evidence from Sackett*

LevelType of evidenceILarge RCTs with clear cut resultsIISmall RCTs with unclear resultsIIICohort and case-control studiesIVHistorical cohort or case-control studiesVCase series, studies with no controls

Open in a separate window

*Adapted from Sackett DL. Rules of evidence and clinical recommendations on the use of antithrombotic agents. Chest 1989;95:2S–4S

Modification of levels

Since the introduction of levels of evidence, several other organizations and journals have adopted variation of the classification system. Diverse specialties are often asking different questions and it was recognized that the type and level of evidence needed to be modified accordingly. Research questions are divided into the categories: treatment, prognosis, diagnosis, and economic/decision analysis. For example, Table 3 shows the levels of evidence developed by the American Society of Plastic Surgeons. [Accessed December 17, 2010]; Available at: http://www.plasticsurgery.org/Medical_Professionals/Health_Policy_and_Advocacy/Health_Policy_Resources/Evidence-based_GuidelinesPractice_Parameters/Description_and_Development_of_Evidence-based_Practice_Guidelines/ASPS_Evidence_Rating_Scales.html.

What is the purpose of affirmative action programs?

Which of the following is one of the distinct categories of police stressors?