Dan Mayer Essential Evidence-based Medicine

What is evidence-based medicine? 15
the outcome of interest
the time frame
(2) Search the medical literature for those studies that are most likely to give
the best evidence. This step requires good searching skills using medical
informatics.
(3) Find the study that is most able to answer this question. Determine the magnitude
and precision of the final results.
(4) Perform a critical appraisal of the study to determine the validity of the
results. Look for sources of bias that may represent a fatal flaw in the study.
(5) Determine how the results will help you in caring for your patient.
(6) Finally, you should evaluate the results of applying the evidence to your
patient or patient population.
The clinical question: structure of the question
The first and most critical part of the EBM process is to ask the right question.
We are all familiar with the computer analogy, “garbage in, garbage out.” The
clinical question (or query) should have a defined structure. The PICO model has
become the standard for stating a searchable question. A good question involves
Patient, Intervention, Comparison,andOutcome. A fifth element, Time,isoften
added to this list. These must be clearly stated in order to search the question
accurately.
The Patient refers to the population group to which you want to apply the
information. This is the patient sitting in your office, clinic, or surgery. If
you are too specific with the population, you will have trouble finding any
evidence for that person. Therefore, you must initially be general in your
specification of this group. If your patient is a middle-aged man with hypertension,
there may be many studies of the current best treatment of hypertension
in this group. However, if you had a middle-aged African-American
woman in front of you, you may not find studies that are limited to this population.
In this case, asking about treatment of hypertension in general will
turn up the most evidence. You can then look through these studies to find
those applicable to that patient.
The Intervention is the therapy, etiology, or diagnostic test that you are interested
in applying to your patient. A therapy could simply be a new drug. If
you are answering a question about the causes of diseases, the exposure to
a potentially harmful process, or risk factors leading to premature mortality,
you will be looking for etiology. We will discuss studies of diagnostic tests in
more detail in Chapters 20–26.
The Comparison is the intervention (therapy, etiology, or diagnostic test)
against which the intervention is measured. A reasonable comparison group