What is EBM?
This module discusses the definition of Evidence Based Medicine or EBM, and the steps in practising EBM.
Searching the medical literature
Reliable, accessible, up-to-date information at the right time.
In this era of information explosion, finding the current best available evidence to answer our clinical question can be very challenging. To do this, we need to develop skills in searching the medical literature efficiently so that we are able to acquire the right information in a timely manner.
Searching for medical literature needs to be done systematically and efficiently especially in the context of limited time. Haynes, et al propose a "5S" hierarchy of information services that can guide us in accessing or searching for information that we need real- or near real-time. Information beginning from systematic reviews are considered to be pre-appraised information because the evidence has already been processed, i.e. assessed for validity and summarized before being made accessible to users.
(For more information on the Haynes' organization of evidence-based information services, click on the "5S" Hierarchy of Information Services button below.)
When searching for evidence, it is recommended that we try to find reliable or trustworthy pre-appraised information first before looking for primary studies. Regardless of the information service we choose to use, whether from the top of the pyramid (e.g. UpToDate) or original studies at the bottom (e.g. a single randomized controlled trial), we need to exert the same due diligence of critically appraising the information that we obtain to ensure that we can reliably apply this in our clinical practice.
Sometimes, we are not able to obtain the information we need from pre-appraised sources. This would mean that we would need to search for evidence from primary or original studies.
There are several electronic databases of medical literature that contain these primary studies. One of the most commonly used is PubMed, which is managed by the US National Library of Medicine. It is one of, if not, the largest database of journal articles, containing more than 25 million articles from more than 5,000 medical journals worldwide. The best thing about it is that it can be accessed for free! Other electronic literature databases include EMBASE, CINAHL, and CENTRAL, among others.
The steps in conducting an efficient literature search are:
1. Identify the concepts in your focused clinical question.
One of the reasons why it is important that we are able to frame our clinical question in terms of the Population, Exposure (which for therapy articles include the Intervention and Comparator), and Outcome(s) is that these concepts (P, E, O, M) can be used as search terms or filters when we do our literature search. An additional concept that we can use as a filter is the study design or Method. Since we would like to identify and retrieve the best available evidence, we should be familiar with what study design would be best suited to answer the type of clinical question we have.
2. Rank/prioritize the concepts.
The next step in doing a literature search is prioritizing the concepts that we will use in our search. We need to ask ourselves which concept (i.e. P, E, O, M) is the most important and will be the first term we will search, and which one is the least important. To help us in deciding, we should ask ourselves, If we were allowed to only search one concept that would ensure that we get the article that we need to answer our clinical question, which concept would that be?
3. Expand or intersect each concept sequentially.
After we have prioritized our concepts, we proceed with the actual electronic literature search. We first expand each concept by combining different search terms (e.g. synonyms, variations in spelling, plural form) using the Boolean operator "OR." Then, we combine different concepts in order of priority by using the Boolean operator "AND." We repeat this sequence until we obtain a manageable number of articles from which we can select the most relevant article for our clinical question.
(For a demonstration on how to do a search on PubMed, click the "Searching the new PubMed" below.)