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Introduction to Evidence Based Medicine

Some Tips

Answering Answerable Questions

Searching Effectively

Critical Appraisal and Properties of Information

This kit was created to aid the practice of evidence-based medicine. Such practice involves the conscientious and judicious use of current best evidence in the healthcare of individuals and populations.

Going through all the processes to make evidence-based decisions can be time consuming, especially if you do not have adequate skills or the time to apply them. Additionally, despite your best efforts, you may not be able to find high quality evidence for many of the clinical decisions you must make.

However, over the last two decades there have been numerous advances in evidence processing, including the production of streamlined guides to aid in critical appraisal of the literature, evidence-based abstraction services, online and other forms of electronic literature searching, growing numbers of high quality systematic reviews, and frequently updated textbooks in paper and electronic formats.

Over time, by learning and practicing critical appraisal and informatics skills, developing a rational and practical approach to uncertainty, and by explicitly incorporating evidence, patient preferences and values into your decision making processes, you will likely become a "connoisseur of evidence". That is, you will develop a taste for continually assessing the evidence upon which you base your clinical decisions, and develop a willingness to seek out and choose high quality pre-appraised and secondary sources of evidence from amongst what is available.

Some Tips

The practice of evidence based medicine can be divided into the following components:

arrowIdentifying a problem or area of uncertainty
arrow Asking a relevant, focused, clinically important question that is answerable
arrow Selecting the most likely resources to search
arrow Searching, and appraising the evidence found
arrow Assessing the clinical importance of the evidence
arrow Assessing the clinical applicability of the evidence
arrow Acting on and appropriately applying the evidence
arrow Assessing the outcomes of your actions
arrow Authoring-summarizing and storing records for future reference

Asking Answerable Questions

The inability to ask a focused and precise clinical question can be a major impediment to evidence-based practice. Clarify clinical questions and consider best potential sources of evidence doing by the following:

1. Ask: "Is this a question about foreground or background knowledge?"

a. Background knowledge questions are general questions about conditions, illnesses, syndromes and patterns of disease, and pathophysiology. They are usually composed of a question root (what,
where, why, when, how) + a verb + a condition.

For example, "What is the typical clinical presentation of Addison's disease?"

A novice more commonly asks this type of question in a
particular knowledge area, in order to gain a general understanding of clinical issues. Best resources include evidence based textbooks and reviews.

b. Foreground questions are more often about issues of care. They query specialized and distinct knowledge needed for specific and relevant clinical decision-making.

Components of a well-built foreground question include "PICOS" (see below). Best resources may include an evidence-based abstraction service, guidelines, systematic reviews, or some evidence-linked textbooks, but may also include the primary literature. The need for skills in searching and critical appraisal is greatest when searching for evidence in the primary literature.

2. Pay attention to the question's component parts, especially for foreground questions,. A useful mnemonic is "PICOS"

a. P patients or populations
b. I interventions
c. C comparison group(s) or "gold standard" or "standard of care"
d. O outcome(s) of interest
d. S study design

3. Classify the question into a domain:
a. Therapy/Prevention
b. Diagnosis
c. Prognosis
d. Harm or Causality/Etiology

4. Ask: "How likely is it that there are high quality summaries or studies with valid and clinically important evidence specifically addressing this issue?"

Searching Effectively

Sources of information and evidence may include:

arrow Textbooks
arrow Journal articles
arrow Guidelines

Where to start searching depends on a number of factors:

arrowAvailable time
arrow Available databases
arrow PICOS and domain of the question asked
arrow Foreground versus background knowledge required
arrow How well the issue lends itself to study

Critical Appraisal and Properties of Information

After completing the search, the results need to be critically appraised. The following are three items that should be looked at:


Attribute Quality
Validity Can I trust this information?
Clinical Importance If true, will the use of this information make an important difference?
Applicability Can I use the information in this instance?