Straus et al. 1 describe evidence-based medicine (EBM) as ‘the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients’. To practice EBM, you must be able to locate the research relevant to the care of your patients, and judge its quality. Only then can you think about applying the findings in clinical practice.
In order to assess the strength of the findings about any particular topic, it is important to recognize that different study designs provide varying levels of evidence relating to the answers obtained from the question posed. These levels may be specified in the following hierarchy (starting with the strongest and leading to the weakest evidence): systematic review or meta-analysis of an RCT → RCT → cohort study → case–control study → cross-sectional survey → case reports → expert opinion → anecdotal information. Note that the hierarchy is not set in stone, as its arrangement depends partly on the problem at hand and partly on the quality of the individual studies themselves. For example, we would choose to perform an RCT to investigate a novel treatment; if, on the other hand, we wish to identify risk factors for a disease outcome, an RCT would not necessarily be appropriate and a cohort or case–control study would provide stronger evidence.
Straus et al. suggest the following approach to EBM. For convenience, we have phrased the third and fourth points below in terms of clinical trials (Chapter 14) and observational studies (Chapters 15 and 16), but they can be modified to suit other forms of investigations (e.g. diagnostic tests, Chapter 38).
1 Formulate the Problem
You must decide what is of interest to you – how you define the patient population, which intervention (e.g. treatment) or comparison is relevant, and what outcome you are looking at (e.g. reduced mortality).
2 Locate the Relevant Information (e.g. on Diagnosis, Prognosis or Therapy)
Often the relevant information will be found in published papers, but you should also consider other possibilities, such as conference abstracts. You must know what databases (e.g. Medline) and other sources of evidence are available, how they are organized, which search terms to use, and how to operate the searching software.
3 Critically Appraise the Methods in order to Assess the Validity (Closeness to the Truth) of the Evidence
The following questions should be asked.
- Have all important outcomes been considered?
- Was the study conducted using an appropriate spectrum of patients?
- Do the results make biological sense?
- Was the study designed to eliminate bias (Chapter 34)? For example, in a clinical trial, was the study controlled, was randomization used in the assignment of patients, was the assessment of response ‘blind’, were any patients lost to follow-up, were the groups treated in a similar fashion aside from the fact that they received different treatments, and was an ‘intention-to-treat’ (ITT) analysis performed (Chapter 14)?
- Are the statistical methods appropriate (e.g. have underlying assumptions been verified, have dependencies in the data such as pairing been taken into account in the analysis)?
4 Extract the most Useful Results and Determine Whether They Are Important
Extracting the Most Useful Results
You should ask the following questions:
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