Study design

What it is

EBM is the best available evidence for diagnosis, prognosis, or treatment. Clinical decision making requires three principles: 1. awareness of the best available evidence, 2. level of evidence, and 3. benefits and risks, burden, and costs. The GRADE approach, Grading of Recommendations Assessment, Development and Evaluation, allows one to rate confidence in estimates of effects. That confidence is rated on four levels: 1. high, 2. moderate, 3. low, 4. very low. The study design it is read against is either randomized or observational. It goes lower with 1. risk of bias, 2. inconsistency, 3. indirectness, 4. imprecision, 5. publication bias; and higher with 1. a large effect, 2. a very large effect, 3. a dose response gradient. The five steps to practice it are 1. ask, 2. acquire, 3. appraise, 4. apply, and 5. act or assess. Worked as a scenario: asking whether a 3-day course of trimethoprim-sulfamethoxazole in adolescents with acute maxillary sinusitis yields the same cure rates as a 10-day course with fewer adverse effects and costs is a therapy question, and its best level of evidence is a systemic review of randomized clinical trial. In practice a recommendation is written together with the quality of the evidence behind it, so that the same guideline carries a strong recommendation on low-quality evidence and a strong recommendation on moderate-quality evidence, each with values and preferences given beside it. Evidence itself is also given a level, as level 2+ or level 2-.