Evidence Based Medicine

This guide is designed to assist health care professionals and students become effective and efficient users of the medical literature.

How are Resources Evaluated?

Following the development of a focused question and discovering the best evidence to answer the question, appraisal is the next step in the Evidence Based Medicine process.

It requires that the evidence found be evaluated for its validity and clinical usefulness. 

Appraisal Concepts - Validity & Reliability

What is validity?

Internal validity is the extent to which the experiment demonstrated a cause-effect relationship between the independent and dependent variables.

External validity is the extent to which one may safely generalize from the sample studied to the defined target population and to other populations.

What is reliability?

Reliability is the extent to which the results of the experiment are replicable.  The research methodology should be described in detail so that the experiment could be repeated with similar results.

More Useful Scientific Terminology

Critically Appraised Topics (CATS)

CATs are critical summaries of a research article.  They are concise, standardized, and provide an appraisal of the research.

If a CAT already exists for an article, it can be read quickly and the clinical bottom line can be put to use as the clinician sees fit.  If a CAT does not exist, the CAT format provides a template to appraise the article of interest.

Find out more about CATS on the LEVELS OF EVIDENCE page.

Evaluating a Study

Start by asking simple questions about the article:

  • Have the study aims been clearly stated?
  • Does the sample accurately reflect the population?
  • Has the sampling method and size been described and justified?
  • Have exclusions been stated?
  • Is the control group easily identified?
  • Is the loss to follow-up detailed?
  • Are enough details included so that the results could be replicated?
  • Are there confounding factors?
  • Are the conclusions logical?
  • Do the findings match the study aims?
  • Can the results be extrapolated to other populations?

Become Familiar with Scientific Experiment Terminology to Aid Your Evaluation

Common Terms:

  • Hypothesis - a statement that is believed to be true but has not yet been tested.
  • Independent variable - the component of an experiment that is controlled by the researcher (for example - a new therapy).
  • Dependent variable - the component of an experiment that changes, or not, as a result of the independent variable (for example - the existence of a disease). 
  • Bias - prejudice or the lack of neutrality.  A systematic deviation from the truth that affects the conclusions and occurs in the process or design of the research.
  • Confounding -a mixing of the effects within an experiment because the variables have not been sufficiently separated.  Possible confounding variables should be discussed in the report of the research.

See also Study Design Terminology on the LEVELS OF EVIDENCE page.

Appraisal Resources

Standards for the Reporting of Scientific/Medical Research


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