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Dignity Health Libraries: Evidence Based Info

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Why is Evidence-Based Medicine Important?

Studies of information-seeking habits of physicians, have shown that when asked, physicians reported that their practice generated about 2 questions for every 3 patients. Only 30% of physicians' information needs were met during the patient visit, usually by a colleague. Reasons for not using printed resources included office textbook collections too old, lack of knowledge of appropriate resources, and lack of time to find the needed information. (Covell DG, 1995)

 When actually observed, investigators found that physicians had about 5 questions for each patient. 52% of these question could be answered by the medical record or hospital information system. 25% could have been answered by published information resources such as textbooks or MEDLINE. (Osheroff JA, 1991)

However, studies have also shown that when clinicians have access to information, it changes their patient care management decisions.

In 1998, Dr. David Sackett, using an "evidence cart" on rounds, reported that of 71 information searches to answer clinical questions, 37 (52%) confirmed the management decision, but 18 (25%) lead to a new therapy or diagnostic test and 16 (23%) corrected a previous plan. (Sackett D, 1998)

Similar results were report by Crowley et al in 2003. The CAR study showed that of 520 clinical questions for which answers were sought in the medical literature, in 53% of these cases the literature confirmed the management decision, but in 47% of these cases the literature changed the medication, diagnostic test, or prognostic information given to the patient. (Crowley S, 2003) 

(Duke University Medical Center Library and Health Sciences Library, UNC-Chapel Hill) 

Evidence-Based Filtered Information

Filtered resources, such as Systematic Reviews / Meta-Analyses, appraise the quality of studies and often make recommendations for practice. For example, authors of a systematic review ask a specific clinical question, perform a comprehensive literature search, eliminate the poorly done studies and attempt to make practice recommendations based on the well-done studies. A meta-analysis is a systematic review that combines all the results of all the studies in a single statistical analysis of results.


Clinical Trials

A clinical trial is any research study that prospectively assigns human participants or groups of humans to one or more health-related interventions to evaluate the effects on health outcomes. Clinical trials may also be referred to as interventional trials. Interventions include but are not restricted to drugs, cells and other biological products, surgical procedures, radiologic procedures, devices, behavioural treatments, process-of-care changes, preventive care, etc

Unfiltered Information

When evidence is not available from filtered resources, then searching the primary literature may be necessary. It is possible to search the primary literature to obtain the highest possible level of evidence.

Resources for Practicing Evidence Based Healthcare

The practice of EBM.

Evidence Pyramid

Use the pyramid to help identify and locate appropriate evidence based resources.  

(Image courtesy of

Evidence Pyramed 

How to Use the Pyramid

Consider the pyramid to be a visual representation of the entirety of clinical biomedical information.  Resources at the bottom of the pyramid are plentiful but are not necessarily Evidence-Based in their approach or findings.  Moving up the pyramid, resources are developed using more robust methodology which lessens bias and leads to stronger Evidence-Based findings but are fewer in number.  The list of resources on the Evidence-Based Resources tab above are listed hierarchically top to bottom based on the pyramid.  Start at the top of the list and move down until you find a resource that answers your question – you can then feel confident that you have discovered the Best Evidence available on your topic.

Levels of Evidence

Levels of Evidence reflect the methodological rigor of studies. A study assigned at Level I Evidnece is considered the most rigorous and least susceptible to bias, while a study deemed to be Level IV Evidence is considered the least rigorous and is more susceptible to bias.

Evidence Focused Search Engines

Developed by Billie White, MLS, Clinical Librarian, St. Joseph's Hospital and Medical Center, Phoenix, AZ