Evidence-based practice

Evidence-based information ranges from Level A (the strongest) to Level C (the weakest).
Level A: randomized controlled trial/meta-analysis
Level B: other evidence
Level C: consensus/expert opinion, clinical practice guidelines

Level A
Randomized controlled trial
A randomized controlled trial (RCT) is the classic "gold standard" study design. Subjects are randomly selected and randomly assigned to groups to undergo rigorously controlled experimental conditions or interventions.

Meta-analysis
A meta-analysis is a study design that uses statistical techniques to combine and analyze data from many studies, usually RCTs.

Level B
Systematic review
A systematic review involves surveying all relevant studies (e.g., quantitative studies, such as RCTs, and qualitative studies, such as observational field studies) to synthesize research results about a specific practice or topic. Strict criteria for review (e.g., highest-level evidence, specific populations, and time range) are used.

Nonquantitative systematic review
A nonquantitative systematic review is a comprehensive survey of all relevant studies that are not numerical (quantitative methods, such as RCTs).

Qualitative study/quantitative study
Qualitative studies explore descriptive, word-based phenomena, such as symptoms, behaviors, culture, and group dynamics. Quantitative studies use statistical methods to establish numerical relationships that are correlational or cause-and-effect.

Nonrandomized clinical trial
A nonrandomized clinical trial might be considered "quasi-experimental": The sample populations aren't randomly selected, the interventions aren't randomly assigned, or both.

Lower-quality RCT
A lower-quality RCT has less strength as evidence because it has less methodologic rigor, resulting in questions of validity. Frequent problems with this type of study include intentional or unintentional bias in sample enrollment; nonblinding, unclear criteria for participant selection; or unreliable or invalid tools.

Clinical cohort study
Clinical cohort studies examine groups of people who have common characteristics or exposure experiences to compare outcomes in those exposed vs. those not exposed (e.g., development of heart disease after exposure or nonexposure to 10 years of secondhand smoke).

Case-controlled study
Case-controlled studies use an observational approach in which subjects known to have a disease or outcome are compared with subjects known not to have that disease or outcome. Subjects are matched on characteristics so that they are as similar as possible except for the disease or outcome.

Uncontrolled study
An uncontrolled study uses design and methods that do not control participant selection or interventions (e.g., a convenience sample, such as patients on a given unit, may be studied because it is the only group reasonably available).

Epidemiological study
Epidemiological studies study people over a long time to determine risk or likelihood of developing diseases. These studies include retrospective database searches or prospective studies that follow a population over time.

Level C
Consensus viewpoint and expert opinion
Consensus viewpoint involves obtaining agreement about specific practices from all clinical experts on a review panel. Expert opinion involves obtaining agreement from a majority of clinical experts on a review panel.

Clinical practice guidelines
CPGs are recommendations for how care should be delivered to people with specific diseases, problems, or situations. Best developed by a panel of clinical and scientific experts, CPGs may be consensus or expert opinion. With sufficient strength of scientific evidence, guidelines are clear. With insufficient evidence, clinical expert opinion can address research gaps. CPGs are the foundation for evidence-based practice and are promising for improving the quality and efficiency of care and patient outcomes.

Meta-synthesis
A meta-synthesis is a systematic review that synthesizes findings from qualitative studies using an interpretive technique to bring small study findings - such as case studies - to clinical application.

Bibliography
Alfaro-LeFevre R. Critical Thinking and Clinical Judgment: A Practical Approach to Outcome-Focused Thinking. 4th ed. St. Louis, MO: Elsevier-Saunders; 2008.

American Academy of Family Physicians. SORT: The strength-of-recommendation taxonomy. AFP website. Available at: w.aafp.org/online/en/home/publications/journals/afp/afpsort.html. Accessed February 18, 2008.

American Academy of Family Physicians. Evidence-based toolkit. AFP website. Available at: www.aafp.org/online/
en/home/publications/journals/afp/ebmtoolkit.html. Accessed February 18, 2008.

Centre for Evidence-Based Medicine. Levels of evidence. CEBM website. Available at: www.cebm.net/
index.aspx?o=1025. Accessed February 18, 2008.

Newhouse RP, Dearholt SL, Poe SS, Pugh LC, White KM. Johns Hopkins Nursing Evidence Based Practice Model and Guidelines. Indianapolis, IN: Sigma Theta Tau International; 2007.

University of Minnesota Twin Cities Bio-Medical Library. Understanding research study designs. University of Minnesota Bio-Medical Library website. Available at: www.biomed.lib.umn.edu/inst/research/pdf. Accessed February 18, 2008.

University of Illinois. Is all evidence created equal? UIC website. Available at: www.uic.edu/depts/lib/lhsp/
resources/levels.shtml. Accessed February 18, 2008.