Practical Nursing

Evidence-based practice involves multiple levels of evidence. Different levels of evidence may carry different levels of weight in order to make informed health-related decisions. Placing studies on this pyramid helps us put the results of a study's design into perspective, based on the strengths and weaknesses of the a study's design. The pyramid takes into account both the quality of evidence and the amount of evidence available.

​Study designs are placed into a hierarchy based on their reliability known as the Levels of Evidence. As you go up the pyramid, each level represents increasing rigor, quality, and reliability of evidence produced by the different types of study design. The levels of evidence are further explained in the Simmons Library Guide. Filtered information has gone through an evaluation process, with clinical experts appraising the evidence. This system for assigning levels of evidence is based from Melnyk and Fineout-Overholt's 2011 book, Evidence-based Practice in Nursing and Healthcare: A Guide to Best Practice. 

Level 1 - Information & opinion

Level 2 - Case studies or case reports

Level 3 - Cohort or longitudinal studies

Level 4 - Randomized Controlled Trials (RCT)

Level 5 - Critically appraised reviews and Reports

Level 6 - Systematic review - Compare all the evidence available

Level 7 - Meta-analysis

DiCenso, A, Bayley, L, Haynes, B. (2009). Accessing preappraised evidence: fine-tuning the 5S model into a 6S model. ACP Journal Club, 15(3). 
New South Wales Health Department. (n.d.). Levels of evidence. Clinical Information Access Portal [CIAP]. https://www.ciap.health.nsw.gov.au/training/ebp-learning-modules/module1/levels-of-evidence.html

Types of Study Design:

• Systematic Reviews & Meta-Analysis

• Double-Blind & Randomized Controlled Trials

• Cohort Studies

• Case-Control Studies

• Case Series & Case Reports

High levels of evidence may not be available or exist yet on certain topics. Less information will be available for more specialized questions with less clinical evidence. 

The top level of the pyramid begins with evidence from Meta-Analysis, including systematic review of results, and methods that are quantitative. A systematic review is when the authors have systematically evaluated and reviewed all available literature and research evidence on a given topic. When multiple authors collaborate to critically appraise, evaluate, and synthesize a number of research studies, they critically appraise a topic. Critically appraising articles involves multiple authors appraising and summarizing individual studies. Randomized Controlled Trials (RCT) groups patients into randomized groups, an experimental group and a control group. The outcomes of interest are followed amongst the groups. Cohort Studies examine two groups or cohorts of patients, those who receive the exposure of interest and those who do not. The outcomes are evaluated over time. Case-control studies identify patients with the outcome of interest and those without the outcome, and then studies the two groups and looks for exposures of interest. Background information or expert opinion evidence is the weakest level of the pyramid. This evidence includes handbooks, encyclopedias, and textbooks. Although these sources are valuable for summarized and foundational knowledge, this information is often generalized information about a topic or condition, as well, it can takes years for this information to be published which can interfere with the currency of evidence-based information. Experts do offer valuable opinions and thoughts on topics, but onions do not hold enough evidence to be considered filtered information. 

References
Winona State University Library. (2019, September 12). Evidence Based Practice Toolkit. Retrieved from https://libguides.winona.edu/c.php?g=11614&p=61584