Applying the Evidence
Once you have determined that a study is internally valid and you understand the findings, you must decide first, based on the outcome you are studying, whether, for example, a specific diagnostic test is available, affordable, and accurate. You must then decide whether the results can be applied to your patient, and how they can further your choice of a management course. If the results are not totally applicable to your patient, you must determine how your patient differs from the subjects of the study and to what extent you can use the findings as a guideline for clinical decisions. If you are considering a therapy, establish whether your patient is similar to or different from the subjects in the study population. You must also, of course, determine how great the benefit of therapy would be for your patient and whether the treatment would meet the patient's expectations. If you are focusing on the possibility of harm, the questions are similar to those for therapy, but you must also determine the patient's risk for adverse effects and whether an alternative therapy might produce less harm. Finally, if prognosis is your main concern, you must ask, again, whether your patient is similar to the study group and, then if and how the evidence will alter your choices for treatment. The above information is summarized in Table 2.
More information on applying the evidence are available:
From the Evidence to Practice , from the WISDOM Project based at the University of Sheffield.
Levels of Evidence and Grades of Recommendations from Oxford University.
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Table 2: Applying the results of a study to individual patient: questions to ask
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Diagnosis
* Is the test affordable, accurate, and available in my hospital? * Can I estimate the pretest probability of the disease in question? * Will the posttest probability affect my management?
Therapy
* Is my patient so different from those in the study group that the results cannot be applied? * According to the study results, how much would my patient benefit from the treatment? * Are the treatment and its consequences consistent with my patient's values and beliefs? Harm * Can the study results be extrapolated to my patient? * What is my patient's risk for adverse effects? * Can my patient's preferences and expectations be met by an alternative therapy?
Prognosis
* Is my patient similar to the patients in the study group? * Will the evidence alter my choice of treatment?
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