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Library 101

Tutorial on information literacy and using the library at FNU

Evidence

You may think of evidence as information that leads you to believe something is true. For example, evidence has to be shown to convict someone of a crime. In health care, we want to see evidence that a particular intervention or treatment will work. This type of evidence is generated by research and made available through scholarly journals, as discussed in the previous section. Importantly, we don't want to see just any evidence, we want to see the best evidence, as noted in the original definition of evidence based medicine.

Evidence Hierarchy

To help determine which evidence is "best," different types of research studies have been organized into a hierarchy, illustrated by a pyramid, with the most reliable evidence at the top and the least reliable at the bottom. Reliability in this sense refers not only to the ability to trust, but also to the ability to reproduce or replicate the evidence. Systematic reviews are considered the most reliable because they are conducted in such a way that someone else can follow the same steps and see if they reach the same conclusion. Anecdotal information is the least reliable because not only cannot it not be verified, personal experiences are usually not repeated exactly.

See the definition of each type of evidence on the pyramid below.

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  1. Systematic Review: An overview of all primary studies on a topic, conducted in a reproducible manner
  2. Meta-Analysis: A statistical study that combines results of several independent studies and recalculates and reanalyzes the data
  3. Critical Appraisal: A summary of evidence to answer a specific clinical question
  4. Randomized Controlled Trial (RCT): A study in which participants are randomly assigned to either a control group or a group that receives a specific intervention; other variables do not come into play
  5. Cohort and Case-Controlled Studies: Both of these studies compare two groups of participants - one with a condition or having received an intervention, one without; a cohort study follows the groups over time, while a case control study looks at their histories
  6. Consensus Statement: A recommendation from a respected authority (e.g. a professional organization)
  7. Anecdotal Information: Information gained from personal experience

You may see other evidence hierarchies or pyramids that are slightly different, but the concept is the same - not all evidence is created equal. It's important to evaluate all information with a critical eye.

Clinical Practice Guidelines

To assist health care providers in their clinical practice, professional organizations will often create clinical practice guidelines to set a standard of care for specific diseases and conditions. These guidelines are created by reviewing and appraising the available evidence to determine the best course of treatment. The recommendations outlined in the guideline should be based on a systematic review. Because they follow a rigorous development process, it takes quite a while for guidelines to be completed and updated.

For more information on clinical practice guidelines, including how to locate them, see the guide below. 

Critical Appraisal

We've mentioned that clinicians need to use the best, most reliable evidence, and that evidence should be evaluated with a critical eye. And we know that step 5 of the EBP cycle is to critically appraise the information found in the previous steps. So how do you do that? You will want to use the information literacy skills you've developed to evaluate research. Tools have been developed to help guide this process. For a list of selected tools, see the link below.