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New England College of Optometry Logo LIBRARY

Evidence-Based Optometry

When No Systematic Reviews or RCTs Exist

You should look for high-quality sources, like a randomized controlled trial (RCT) or systematic review, to answer your foreground question.

However, although some studies are of a higher quality than others (as seen on the evidence pyramid), some scientific studies are better at answering specific types of questions. 

  • Prognosis: Cohort study
  • Diagnosis: Cross‐sectional study
  • Etiology: Cohort or case-control study
  • Harm (Is the intervention being studied harmful?): Cohort study, RCT, or case-control study
  • Rare Diseases:

For rare diseases, it is actually best to examine case studies, despite their location at the bottom of the evidence pyramid. This is because sometimes a disease is so rare there aren't enough participants for a randomized controlled trial to be conducted.

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