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Hierarchy of Evidence

Rob (PHH)

The hierarchy of evidence is a phrase used to describe the "quality" of research supporting (or not supporting) a scientific idea or treatment. The hierarchy of evidence is also a tool we can use to evaluate study designs, and thereby the risks of bias from those studies' conclusions.


When navigating hair loss treatments, it is critical to understand the hierarchy of evidence. This is because hair loss treatments that are supported by "lower quality" studies are at a higher risk of those studies' "clinical results" not aligning with the real-world experiences of people trying those treatments.

Conversely, the higher up the hierarchy we climb, the more likely it is that an intervention's "clinical results" match the real-world results of its users.

This is a particularly important concept for people trying to choose between "conventional" vs. "natural" hair loss treatments. For instance, while personal preferences should always dictate treatment choices, factors such as hair loss speed should also act as critical determinants for which treatments to prioritize, and what the opportunity costs might be for you should you try lesser-supported treatments and fail to see results. The hierarchy of evidence creates a framework to assess these decisions.

For more information, see these resources:

  • Evidence hierarchy
  • hierarchies of evidence
  • evidence quality
  • quality of evidence
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