Levels of evidence

  1. Meta-Analysis: A systematic review that uses quantitative methods to summarize the results
  2. Systematic Review: Authors have systematically searched for, appraised, and summarized all of the medical literature for a specific topic
  3. Critically Appraised Topic: Authors evaluate and synthesize multiple research studies
  4. 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
  5. 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
  6. 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
  7. Background Information/Expert Opinion: Handbooks, encyclopedias, and textbooks often provide a good foundation or introduction and often include generalized information about a condition