PAS 5302 - Evidence-based Medicine and Research: Evidence-Based Medicine

Levels of Evidence in Evidence-Based Practice

Number and explanation of levels vary by author. However, it is generally agreed that Level 1 - and, to some extent, Level 2 - indicate the best research for Evidence-Based Practice.

The Levels of Evidence are:

1. Systematic review or meta analysis of all relevant randomized controlled trials
2. Randomized controlled trial
3. Single well-designed controlled trial without randomization
4. Cohort and case-control studies
5. Meta-synthesis of descriptive/qualitative studies
6. Single descriptive or qualitative study
7. Expert opinion and anecdotal evidence
8. Animal research and in-vitro studies

The levels in the above list have been adapted from the following excellent resources:

In evidence-based practice, PICO formatted questions (sometimes styled PICOT) assist nurses and other health professionals in developing effective and efficient search parameters that produce high quality, specific, and evidence-based results.

PICO(T) stands for:

• P = Patient, Population or Problem - Who is to be treated? What is the issue requiring treatment?
• I = Intervention or exposure - What is the expected treatment?
• C = Comparison - Is there another treatment (or no treatment) to be considered?
• O = Outcome - What is the desired result of the treatment?
• T = Time-frame (optional) - How long is the intervention (or study) expected to take?

The following resources explain the PICO process and provide guidance in precise formulation of PICO questions.

Using Filters to Find EBM Articles in Health Science Databases

 
MEDLINE

On the MEDLINE (EBSCO) Advanced Search page, scroll down to the Filter column beneath the search boxes. Check the boxes before EBM Reviews and Systematic Reviews, enter your search terms, and select the Search button.

Alternatively, from the search results page, select the Filters menu, which will display on the right side of the page. Check the box before EBM Reviews, then select the Apply button.

CINAHL Complete

On the CINAHL Complete Advanced Search page, scroll down to the Filter column beneath the search boxes. Check the box before Evidence-Based Practice, enter your search terms, and select the Search button.

ClincalKey

On the ClinicalKey home page, select the Journal option from the All Types dropdown menu. Enter your search terms and select the Search button.

On the results page, check the Meta-analyses option from the Filter By sidebar on the left side of the page. The results will reload with the selected filter. 

• Systematic Review - Review article that attempts to eliminate bias by focusing on a single question and using a formal, scientific methodology for literature analysis. Best resource for evidence-based practice.
• Meta Analysis - Synthesis of quantitative data from multiple independent studies; may be the data component of a systematic review.
• Randomized Controlled Trial - Research in which participants are randomly assigned to groups as a means of comparing interventions or treatments. One group acts as the control and receives standard treatment, no treatment, or placebo. 
• Cohort Study - Observational research method that follows a group of individuals with a shared characteristic for a set period of time to evaluate a health outcome or development.
• Case-control Study - Retrospective observational study, similar to cohort study, where researchers examine case histories of a group of individuals with a specific disease or disorder in comparison with a group who does not. 
• Meta Synthesis - Synthesis of qualitative data to develop a new interpretation or comprehension of a research topic; may lead to the development of new lines of research or new theories.  
• Research Article - Original research performed by the author; includes methodology, data collection and/or analysis, and a discussion of results.
• Review Article - Examination and overview of previously published works; summarizes, compares, and interprets findings. May be biased if not done systematically.
• Quantitative Research - Objective data collection and analysis; focuses on numerical data.
• Qualitative Research - Collection and analysis of non-numerical data; utilizes interviews, surveys, and observational studies.

Additional information about systematic reviews: