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Evidence-Based Practice

Finding Evidence

Evidence refers to information that healthcare providers use to weigh options and make clinical decisions with patients such as prescribing medications, ordering tests, or choosing a surgical procedure.

Evidence comes in various forms:

  • Clinical Practice Guidelines: These are recommendations developed by expert panels based on a comprehensive review of the evidence and provide guidance on best practices.
  • Systematic Reviews and Meta-Analyses: These are studies which synthesize results from multiple studies to provide a high level of evidence on a particular question.
  • Clinical Research Studies: These include scientific studies conducted in the form of randomized controlled trials (RCTs), cohort studies, and case-control studies that provide data gathered through observation/experimentation on the efficacy and safety of treatments and diagnostic tests or procedures.
  • Patient Data: A patient’s medical history and preferences should be integrated with scientific evidence to ensure that clinical decisions are tailored to the needs of the patient.
  • Clinical Expertise and Judgement: Not every clinical scenario fits neatly into clinical practice guidelines or research studies. Healthcare providers have first-hand knowledge of their patients’ circumstances and have years of hands-on experience adapting evidence to their patient’s unique needs and preferences.

Is all evidence equal?

Research studies serve as the foundation for clinical evidence, but not all studies are conducted with the same rigor. Additionally, while a study may have been conducted using rigorous methods, it may not be relevant to your clinical question.

Reliability refers to the consistency and dependability of research study results. In EBP, it is crucial to carefully consider the reliability of evidence to ensure that research findings are not due to random chance, error, or specific circumstances.

Here's what to consider:

  • Repeatability: If a study was repeated in a different setting or context, or with a different population, what is the likelihood that the results would be the same?
  • Accuracy: Was the study conducted in a way that ensures measurements and observations are accurate and free from significant errors that could have impacted the results?

Relevance refers to the applicability of research findings to a specific context, patient or population. 

Consider the following:

  • Study Participants: Look at the demographics, health status, and other relevant characteristics of study participants to see if they align with those of your patient or target population.
  • Intervention(s) and Outcomes: Did the study test the intervention(s) of interest and measure the health outcomes relevant to your patient or target population?

Source: American Medical Association, Guyatt G, Rennie D, Meade M, Cook D. Users' Guides to the Medical Literature: A Manual for Evidence-based Clinical Practice. 3rd ed. McGraw-Hill Education; 2015.

Evidence pyramids or hierarchies aim to rank the strength and reliability of sources of evidence in healthcare. The concept is that as you advance up the hierarchy, the "level of processing" and number of experts involved in generating the evidence increases, therefore this minimizes the risk of bias.

While focusing your search on a specific level of evidence can be helpful, clinicians should remember that the level of evidence does not always equate to quality. Regardless of study design or level of evidence, each source should be evaluated for its quality.

The 6S Model of Levels of Evidence

Systems
 Standards of care and recommendations from clinical decision support systems (e.g., EHR systems)
Summaries
 Clinical practice guidelines and clinical topic summaries
Synopses of Syntheses
 Summaries of a systematic review with commentary and a critical appraisal component
Syntheses
 Systematic reviews
Synopses of Studies
 Summaries of a single study with commentary and a critical appraisal component
Studies
 Original clinical research articles published in journals

Levels of Evidence (Primary Studies) by Question Type

The approach to finding evidence should be tailored to the specific clinical question. Certain study designs are best suited for specific types of questions. For example, randomized controlled trials (RCTs) are ideal for assessing treatment efficacy, while cohort studies and case-control studies are better for understanding prognosis and risk factors. The hierarchy below can help clinicians find the most appropriate studies to answer a clinical question.

The Critical Appraisal Skills Programme (CASP) Glossary provides definitions of evidence-based practice terminology and explanations of study designs.

Question Type
Optimal Study Designs
Search Strategies

The links below will launch broad search strategies in PubMed Clinical Queries for each question type. Refine the search by adding more terms to the search bar related to your PICO question.
Therapy

Randomized controlled trials
Observational studies (cohort, case-control)

Therapy: PubMed Clinical Queries
Diagnosis

Blind, prospective study that compares one diagnostic method to a another (gold standard)

 Diagnosis: PubMed Clinical Queries
Prognosis

Randomized controlled trials
Observational studies (cohort, case-control)

 Prognosis: PubMed Clinical Queries

Other Evidence Ranking Systems

There are many other ranking systems describing the levels of evidence. Each system has its own criteria and methodology, but they all aim to help healthcare professionals make informed decisions based on the best available evidence.

1. AACN (American Association of Critical-Care Nurses) Levels of Evidence: Structured in an alphabetical hierarchy from A-E and M. “Levels A, B, and C are based on research (either experimental or nonexperimental designs) and are considered evidence. Levels D, E, and M are considered recommendations drawn from articles, theory, or manufacturers’ recommendations. (AACN)

2. Joanna Briggs Institute (JBI) Levels of Evidence: Categorizes evidence according to the type of clinical question (eg. treatment, diagnosis, prognosis) with a focus on systematic reviews, randomized controlled trials, and qualitative research.

3. Oxford Centre for Evidence-Based Medicine (OCEBM) Levels of Evidence: Recommends study designs based on the type of clinical question to be answered. Stratifies study designs from strongest to weakest based on their susceptibility to bias.

5. Strength of Recommendation Taxonomy (SORT): Developed by the American Academy of Family Physicians (AAFP), SORT categorizes studies into 3 levels based on the type of clinical question, study design, and study quality.

6. The U.S. Preventive Services Task Force (USPSTF): The USPSTF monitors and appraises clinical research studies to develop recommendations related to primary care and prevention based on a body of evidence. USPSTF uses a grading system (A, B, C, D, or I) to score the collective strength of evidence supporting USPSTF recommendations.

Sources:

American Medical Association, Guyatt G, Rennie D, Meade M, Cook D. Users' guides to the medical literature: A manual for evidence-based clinical practice. 3rd ed. McGraw-Hill Education; 2015.

Dicenso A, Bayley L, Haynes RB. Accessing pre-appraised evidence: fine-tuning the 5S model into a 6S model. Evid Based Nurs. 2009;12(4):99-101. doi:10.1136/ebn.12.4.99-b

Clinical topic summaries combine the best available research on specific clinical questions or topics to offer practical recommendations for clinicians. The databases listed below provide summaries that often include references to clinical practice guidelines. While not every clinical question will have an associated summary or guideline, checking these databases should be your first step in the process.

Clinical practice guidelines are grounded in the latest research and expert consensus and aim to enhance patient outcomes and standardize healthcare practices.

Numerous professional societies and organizations, such as the American College of Cardiology, American Academic of Pediatrics, and the Infectious Disease Society of America, regularly develop and update guidelines to assist healthcare providers in delivering evidence-based care.

The databases listed below search across multiple societies to identify relevant practice guidelines.

  • ECRI Guidelines Trust is a publicly accessible online repository that provides healthcare professionals with reliable, evidence-based clinical practice guidelines. Developed by ECRI, a nonprofit organization, this resource includes guidelines from various medical organizations and specialty societies.
  • Trip (Turning Research Into Practice) is a clinical search engine designed to allow users to quickly and easily find and use high-quality research evidence to support their practice and/or care. Trip indexes guidelines published by societies and organizations.
  • UpToDate Society Guidelines by Specialty includes links to guidelines for each specialty. After entering UpToDate, go to Contents > Topics by Specialty. Then select the specialty of interest and find the Society Guidelines link. This will take you to a list of guidelines organized by topic.
  • US Preventive Services Task Force (USPSTF) publishes evidence-based recommendations about clinical preventive services such as screenings, counseling services, and preventive medications. All recommendations are published on the Task Force’s Web site.

Clinical Practice Guidelines by Topic or Specialty
 

Cardiology American College of Cardiology (ACC) Guidelines and Clinical Documents
Diabetes American Diabetes Association (ADA) Standards of Care
Gastroenterology American College of Gastroenterology (ACG) Guidelines
Infectious Disease Infectious Diseases Society of American (IDSA) Practice Guidelines
OBGYN American College of Obstetrics and Gynecology (ACOG) Clinical Practice Guidelines
Oncology National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines
Orthopedics American Academic of Orthopedic Surgeons (AAOS) Clinical Practice Guidelines
Psychiatry
(Child & Adolescent)		 American Academy of Child & Adolescent Psychiatry (AACAP) Clinical Practice Guidelines
Psychiatry
(General)		 American Psychiatric Association (APA) Clinical Practice Guidelines

Pre-appraised studies are articles that summarize and appraise new studies that have the potential to influence research or transform healthcare practice. These articles are often published in evidence-based practice (EBP) journals as well as many of the core clinical journals.

Examples: 

What is a systematic review?

A systematic review is a study designed to answer specific clinical questions by comprehensively collecting and critically analyzing multiple research studies on a particular topic. Here’s how it works:

  1. Formulating a Clear Question: The process begins with a well-defined clinical question, often framed using the PICO format (Population, Intervention, Comparison, Outcome).

  2. Comprehensive Literature Search: Researchers conduct an exhaustive search of relevant databases to gather all available studies that address the question.

  3. Study Selection and Appraisal: The gathered studies are then screened for relevance and quality. Only those meeting predefined criteria are included in the review.

  4. Data Extraction and Synthesis: Data from the selected studies are extracted and synthesized, often using statistical methods to combine results in a meta-analysis.

  5. Interpretation and Conclusions: The findings are interpreted in the context of the clinical question, providing a high level of evidence to inform clinical decision-making.

Find Systematic Reviews

Finding Studies in PubMed

If you cannot answer a clinical question using a clinical practice guideline or summary, or if you wish to explore the evidence in more detail, the next step is to search a database for original research. PubMed is a good starting point, but other databases may be useful.

These strategies can help you effectively search databases for studies that are relevant to your clinical question. This 30-minute tutorial on Using PubMed in Evidence-Based Practice demonstrates how to apply the tips below to your search.

  1. Use PICO to Identify Search Terms: Use the PICO framework to break down your clinical question into the concepts to be searched. Then identify keywords for each concept including synonyms and related terms to broaden your search.

  2. Combine Keywords with Boolean Operators: Use AND, OR, and NOT to combine your concepts and keywords effectively. For example, (diabetes AND insulin) or (hypertension OR high blood pressure).

  3. Apply Filters: Use PubMed search filters to narrow down your results. Filters can include publication date, age group, and language. The article type filter may be useful in focusing your search on a specific study design and level of evidence (e.g., randomized controlled trials, systematic reviews, and practice guidelines).

  4. Use MeSH Terms: In PubMed, use Medical Subject Headings (MeSH) to find articles indexed with specific terms. This can improve the relevance of your search results. This tutorial, Topic Searching in PubMed: Using the Medical Subject Headings (MeSH) explains how to use MeSH to enhance your search with additional terms.

  5. Check Reference Lists: Look at the reference lists of relevant articles to find additional sources that might be useful.

  6. Use Advanced Search Options: Utilize advanced search features to refine your search. This can include field-specific searches (e.g., title, abstract).

  7. Save and Organize Results: Use tools like PubMed’s “My NCBI” or Zotero to save and organize your search results for easy access later.