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HSC 310 - Evidence Based Health Care: Levels of Evidence

Levels of evidence

Evidence hierarchies can help you strategically identify which resources to use for finding evidence, as well as which search results are most likely to be "best".

The image is taken from the book, Essentials of Evidence-Based Nursing Practice, p.23 (2018). It shows that the strongest evidence at the top, is systematic reviews, "because the strongest evidence comes from careful syntheses of multiple studies (23)."

Evaluating Scientific Research Worksheet

Secondary Source Examples

The AUTHOR did NOT do the study/experiment her/himself.

  • Reviews the results of several experiments or trials
  • Analysis of a clinical trial
  • Reviews, systematic reviews, meta-analysis
  • Newsletters and professional news sources
  • Practice guidelines & standards
  • Clinical care notes
  • Patient education Information
  • Government & legal Information
  • Monographs
  • Entries in nursing or medical encyclopedias

Primary Source Examples

The AUTHOR  did the research, conducted the study, or ran the experiment; Includes the hypothesis, methodology, and results sections

  • Papers and proceedings from scientific conferences or meetings
  • Dissertations and Theses
  • Technical Reports, Lab Reports
  • Patents, Pilot Studies, Survey research, Case Studies, Cohort Studies

Types of Research Explained

3 places an article will mention what type of study was done: 

  1. The title
  2. The abstract
  3. The methods section of the article.

Systematic Review
Uses explicit, rigorous methods to identify, critically appraise, and synthesize multiple studies on a topic (the strongest type of evidence). 

Meta Analysis
A type of systematic review, that uses a quantitative method to statistically combine the results of many studies and synthesize their conclusions together.

Randomized controlled trial
A clinical trial that involves at least one test treatment and one control treatment, concurrent enrollment and follow up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process.

Prospective, blind comparison to a gold standard
A controlled trial that compares a new diagnostic tool/test to what is currently considered the "goal standard."

Cohort Study
Study in which subsets of a defined population are identified and studies over a period of time to see the effects of something.

Case Control Studies
Study uses cases with a certain condition, such as kidney disease, and compares it to control cases without the condition.

Case Series / Reports
Articles written about one patient or a series of patients with the same issue. Great for rare diseases, disorders, and drug/treatment reactions (Not the best source of evidence because it focuses on a small group of people).