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Evidence-Based Practice: Understanding the Hierarchy and Strength of Evidence
Evidence-Based Practice (EBP) requires healthcare professionals to identify and apply high-quality research data to make clinical decisions. Evidence-based practitioners must determine the strength of the evidence they find in the literature, as systems for rating the strength of evidence vary widely. To assist in this process, the highest or strongest levels of evidence appear near the top of the Evidence Pyramid, and can be harder to find (if such evidence exists at all).
Understanding the Hierarchy of Research Designs
Not sure where on the evidence pyramid to place an article you have found? Not sure what type of study design is being used? Levels of evidence are determined by several critical factors:
- Strength of Evidence: confidence that the evidence is a true measure.
- Quality of Evidence: minimization of bias.
- Statistical Precision: degree of certainty about the existence of a true measured effect.
- Size of Effect: how much of an effect is above 'No Apparent Effect' for clinically relevant benefits.
- Relevance of Evidence: appropriateness of the outcome measure and usefulness in measuring benefits or harms.
The Levels of Evidence Hierarchy
| Level | Study Design Type |
|---|---|
| Highest Level | Systematic review of all relevant randomized controlled trials (RCTs). |
| Next Highest Level | At least one RCT on effectiveness. |
| Intermediate Level | A pseudo-randomized trial that assigns participants by alternating between groups by date of admission. |
| Lower Levels | Non-randomized studies with control group running concurrently with intervention group. |
| Lower Levels | Non-randomized studies with intervention effects which are compared to previous / historical information. |
| Base Level | Single-case studies. |
Secondary Sources and Summaries
Secondary sources are summaries and analyses of the evidence derived from and based on primary sources. They provide an appraisal of the quality of studies and often make recommendations for practice. Several types of studies are considered secondary sources:
Clinical Practice Guidelines (CPGs) are practice recommendations based on the best available evidence written by healthcare organizations. Guidelines are meant as recommendations for evidence-based patient care.
Systematic Reviews (SRs) focus on peer-reviewed publications about a specific problem. Rigorous, standardized methods for selecting and assessing articles are used to limit bias in the assembly, critical appraisal, and synthesis of all relevant studies on a specific topic. A systematic review may or may not include a Meta-Analysis (MA), which is a quantitative summary of the results.
Critically Appraised Topics (CAT) are short summaries of the best available evidence, created to answer a specific clinical question. It is like a concise and less rigorous version of a systematic review.
Rating Tools and Resources
To evaluate the literature, professionals can use the Johns Hopkins Nursing Evidence Rating Scales to rate the strength of evidence. Additionally, various databases provide access to high-quality information:
- AHRQ's National Guideline Clearinghouse: A public resource for summaries of evidence-based clinical practice guidelines.
- National Institute for Health and Care Excellence (NICE): Provides national guidance and advice to improve health and social care.
- PEDro: A free database of over 35,000 randomised trials, systematic reviews and clinical practice guidelines in physiotherapy. All trials on PEDro are independently assessed for quality.
- BETs: Designed specifically for Emergency Medicine, the BET method allows the use of lower quality research and lists the shortcomings of the evidence used.
When analyzing results, practitioners should look for the Confidence Interval (CI), which covers the likely range of true effect, noting that the play of chance can skew results.