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Originally Published MD&DI April 2007

CLINICAL TRIALS

Clinical Evidence Hierarchies

Sidebar:
Both FDA and CMS rely on hierarchies for assigning weight to clinical data. For example, in 21 CFR 860, FDA lists the following as its preferred clinical documents in descending order of importance:
  • Well-controlled investigations.
  • Partially controlled studies.
  • Studies and objective trials without matched controls.
  • Well-documented case histories conducted by qualified experts.
  • Reports of significant human experience with a marketed device.

CMS employs a similar evidence hierarchy. An example of this is its decision memorandum for NCD’s implantable cardiovertor-defibrillators, issued in June 2003. The NCD offers “a representative list of study designs ranked from most to least methodologically rigorous in their potential ability to minimize systematic bias” as follows:

  • Randomized controlled trials.
  • Nonrandomized controlled trials.
  • Prospective cohort studies.
  • Retrospective case control studies.
  • Cross-sectional studies.
  • Surveillance studies (e.g., using registries or surveys).
  • Consecutive case series.
  • Single case reports.

Note that the randomized controlled trial (or what FDA calls a well-controlled investigation), is at the top of both lists.

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