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Evidence Based Practice Tutorial

Step 3: Appraise

  • Once you've started doing some searches, it's time to determine if the sources you're finding are relevant to your research, appropriate for your writing, and meeting the requirements of your field or course. 
  • Make sure your sources actually say what you think they say. It can be tempting to skim through complex articles when writing academic assignments, but the last thing you want is to misrepresent the ideas in a study or have a faulty understanding of the evidence. Be able to briefly sum up the article and explain why you're using that article specifically in your writing.
  • Additionally, you'll want to make sure you're using the right kinds of evidence to support the type of research question you're answering. In some fields, the differences between types of studies are less important, but in others, particularly health care, those distinctions are crucial. 
  • Check out the boxes below for more information about evidence tables/matrices, hierarchies of evidence, and clinical study categories.

Further reading for Step 3: Appraise

Hierarchies of Evidence

Appraising the Evidence

  • Each field has a hierarchy of evidence, meaning that some types of studies provide higher levels of evidence than others. Typically, the studies with the highest level of evidence will be large compilations of many other studies, like meta-analyses and systematic reviews, and the type of study is usually indicated in the article title.
  • The other tabs in this box are health care-specific hierarchies of evidence and while they are most commonly used in nursing, they are broadly applicable across other health care disciplines like psychology and social work.

Level 1

Systematic reviews of RCTs
Current practice guidelines

Level 2

Randomized controlled trials    

Level 3

Controlled trials without randomization (quasi-experimental)      

Level 4

Cohort studies (epidemiologic)
Case-controlled studies (epidemiologic)

Level 5

Systematic review of descriptive studies
Systematic review of qualitative studies (meta-synthesis)
Correlational studies

Level 6

Single descriptive study
Single qualitative study
Caser series studies (epidemiologic)
Case reports
Concept analysis

Level 7

Opinion of authorities
Reports of expert committees
Manufacturer's recommendations
Traditional literature reviews
Animal Research

Types of studies


  • Works that summarize the results of multiple studies on a topic and mathematically combine the results using accepted statistical methodology to report the results as if it were one large study.

Systematic Reviews

  • A summary of evidence on a particular topic that uses a rigorous process (to minimize bias) for identifying, appraising, and synthesizing multiple research studies. Examples of these types of reports can be found in the Cochrane Library database.

Randomized Control Trials

  • A true experiment that delivers an intervention or treatment in which subjects are randomly assigned to control and experimental groups. RCTs are the strongest design to support cause and effect relationships.

Cohort Studies

  • Longitudinal studies that begin with two groups of patients (the cohorts), one that received an exposure and one that does not. The groups are then followed over time to measure the development of different outcomes. Cohort studies are observational and the two groups may differ in ways other than the variable under study.

Case-Control Studies

  • Studies in which patients who already have a specific condition are compared with people who do not. The researcher looks back to identify factors or exposures that might be associated with the illness. They often rely on medical records and patient recall for data collection. These types of studies are often less reliable than randomized controlled trials and cohort studies because showing a statistical relationship does not mean that one factor necessarily caused the other.

Case series and Case reports

  • Collections of reports on the treatment of individual patients or a report on a single patient. Because they are reports of cases and use no control groups to compare outcomes, they have little statistical validity.

Animal Research

  • Studies that use animals as investigational subjects.


Therapy (Intervention) or Diagnosis

  1. Systematic review or meta-analysis of randomized controlled trials (RCTs)
  2. RCTs
  3. Non-RCTs
  4. Cohort studies or case-control studies
  5. Meta-synthesis of qualitative or descriptive studies
  6. Qualitative or descriptive single studies
  7. Expert opinion

Etiology/Harm or Prognosis

  1. Synthesis of cohort study or case-control studies
  2. Single cohort study or case-control studies
  3. Meta-synthesis of qualitative or descriptive studies
  4. Single qualitative or descriptive studies
  5. Expert opinion


  1. Meta-synthesis of qualitative studies
  2. Single qualitative studies
  3. Synthesis of descriptive studies
  4. Single descriptive studies
  5. Expert opinion