Evidence-Based Medicine

Definition/Introduction

Evidence-based medicine (EBM) uses the scientific method to organize and apply current data to improve healthcare decisions. Thus, the best available science is combined with the healthcare professional's clinical experience and the patient's values to arrive at the best medical decision for the patient. There are 5 main steps for applying EBM to clinical practice:

• Defining a clinically relevant question
• Searching for the best evidence
• Critically appraising the evidence
• Applying the evidence
• Evaluating the performance of EBM  [1][2][3]

EBM starts with a clinical question. The clinical question is an issue that the healthcare provider addresses with the patient. After the clinical question is formulated, relevant scientific evidence is sought, which relates to the clinical question. Scientific evidence includes study outcomes and opinions. Not all data has the same strength. Recommendations from an expert are not as robust as the results of a well-conducted study, which is not as good as those of a set of well-conducted studies. Thus in evidence-based medicine, the levels of evidence or data should be graded according to their relative strength. Stronger evidence should be given more weight when making clinical decisions.

The evidence is commonly stratified into 6 different levels: 

• Level IA evidence is obtained from a meta-analysis of multiple well-conducted and well-designed randomized trials. Randomized trials provide some of the strongest clinical evidence, and if these are repeated and the results are combined in a meta-analysis, then the overall results are assumed to be even stronger.

• Level IB evidence is obtained from a single well-conducted and well-designed randomized controlled trial. When well-designed and well-conducted, the randomized controlled study is a gold standard for clinical medicine.

• Level IIA evidence is from at least one well-designed, executed, non-randomized controlled study. When randomization does not occur, there may be more bias introduced into the study. 

• Level IIB evidence is from at least one well-designed case-control or cohort study. A randomized controlled study cannot effectively or ethically study all clinical questions. 

• Level III evidence is from at least one non-experimental study. Typically, it would include case series, not well-designed case-control or cohort studies.   

• Level IV includes expert opinions from respected authorities on the subject based on their clinical experience.

All clinical studies or scientific evidence can be classified into one of the above categories. The clinician must then use their professional, clinical experience to extrapolate the scientific evidence as it applies to the specific patient. Most clinical studies have specific inclusion and exclusion criteria and the specific population studied. More often than not, the patient being treated by the clinician will have one or more substantial differences from the population in the study. The medical provider must then use their clinical judgment to determine how the variations between the patient and the study population are important or not and how they affect applying the study results to the specific patient.

For example, a specific patient may be a 70-year-old female with a history of hyperlipidemia and a new diagnosis of hypertension, looking at hypertension treatment options. The clinician may find a good randomized controlled trial looking at medications to control hypertension, but the study's inclusion criteria were a population of 18 to 65-year-olds. Should the clinician ignore the results as the specific patient does not meet the study demographics? Should the clinician ignore the age difference between the specific patient and the study population? This is where the clinical judgment helps bridge the gap between the relevant scientific evidence and the specific patient being treated.

Finally, clinicians using evidence-based medicine must put all of the information in the context of the patient's values or preferences. The patient's values or preferences may conflict with some of the possible options. Even strong evidence supporting a specific treatment may not be compatible with the patient's preferences, and thus, the clinician may not recommend the treatment to the patient. Also, the treatment might not apply to the specific patient. As an example, a patient may have a particular form of cancer. Level IA evidence may suggest life expectancy can double from 8 to 16 months with chemotherapy. Chemotherapy has significant side effects. The patient may find those side effects not acceptable and elect not to pursue chemotherapy secondary to the specific patient's preferences and values.

The outcome must be evaluated once the clinical question is formulated, relevant scientific information is evaluated, and clinical judgment is used to apply the relevant scientific evidence to the specific patient and their values. The final step is a re-evaluation of the patient and clinical outcome after the application of the applied information. Did the intervention help? Were the outcomes as expected? What new information is obtained? How can this information be applied to future situations and patients? Evidenced-based medicine starts with the clinical question and returns to the clinical question at the end to see how the process works. Without continuous re-evaluation, the medical provider will be unsure if their impact is positive or negative. Evidence-based medicine is a perpetual wheel of improvement rather than a one-time linear process.

Issues of Concern