The hierarchy of evidence reflects the relative weight given various types of scientific evidence. It plays an important part in evidence-based practice, especially evidence-based medicine. The hierarchy, listed from the best forms of evidence to the worst, is as follows:

1. • Systematic reviews of randomised controlled trials, often using meta-analysis
   • Randomised controlled trials
   • Cohort studies (also known as prospective studies)
   • Case-control studies
   • Case studies
   • Expert opinion
   • Anecdotal evidence