Step 4 in evidence-based practice is about applying research evidence to the individual patient and clinical decision making. As described by Chang et al., study participants and real world patients are likely to differ by degree, rather than grossly, in their response to treatment. Individualizing treatment decisions involves estimation of the balance of risks and benefits, combined with a consideration of patient values. The number needed to treat (NNT) is the number of patients that need to be treated to prevent one additional adverse event, and it is the inverse of the absolute risk reduction. The number need to harm (NNH), in contrast, is the number of patients treated who would be expected to experience one adverse event. NNT and NNH illustrated the balance between benefits and risks of a given intervention; in oncology, this is particularly relevant with to screening, which may result in harms from follow up of false positives, and treatment, which often produces dose-dependent toxicity.
Levels of decision making:
Dr. Leon Gordis (Johns Hopkins University) described the following levels of decision making on applying evidence to a particular patient.
- Level 1: "would you have this done for yourself or for someone else in our immediate family?" Influenced by one's personal experience with disease and capacity to deal with risk.
- Level 2: "would you make this recommendation for your own patient?" Clinicians engage in informed and shared decision making with patient. Influence by prior experience, but the strength of the scientific evidence may play a greater role.
- Level 3: "would you make and across-the-board recommendation for a population?" Must be based on rigorous assessment of the scientific evidence.
Resources for EBM as shared decision making:
Levels of evidence:
The National Cancer Institute defines levels of evidence as "a ranking system used to describe the strength of the results measured in a clinical trial or research study. (such as a case report for an individual patient or a double-blinded randomized controlled trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence."
As you move up the pyramid, however, fewer studies are available; it is important to recognize that high levels of evidence may not exist for your clinical question. If this is the case, you will need to move down the pyramid if your quest for resources at the top of the pyramid is unsuccessful.
- Meta-Analysis: A systematic review that uses quantitative methods to summarize the results.
- Systematic Review: Authors have systematically searched for, appraised, and summarized all of the medical literature for a specific topic.
- Critically Appraised Topic: Authors evaluate and synthesize multiple research studies.
- Critically Appraised Articles: Authors evaluate and synopsize individual research studies.
- Randomized Controlled Trials: Include a randomized group of patients in an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.
- Cohort Study: Identifies two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
- Case-Control Study: Identifies patients who have the outcome of interest (cases) and control patients without the same outcome, and looks for exposure of interest.
- Background Information/Expert Opinion: Handbooks, encyclopedias, and textbooks often provide a good foundation or introduction and often include generalized information about a condition. While background information presents a convenient summary, often it takes about three years for this type of literature to be published.
- Animal Research/Lab Studies: Information begins at the bottom of the pyramid: this is where ideas and laboratory research takes place. Ideas turn into therapies and diagnostic tools, which then are tested with lab models and animals.
Resources for level of evidence: