Evidence Tier
A ranking system that grades the strength and reliability of scientific evidence supporting a treatment, from the strongest (large randomized controlled trials and meta-analyses) to the weakest (expert opinion and animal studies). Understanding evidence tiers helps patients and providers assess how confident they can be in a treatment's reported benefits.
Related Terms
Clinical Trial
A carefully designed research study conducted in human volunteers to evaluate whether a treatment is safe, effective, and better than existing options. Clinical trials progress through phases (I through IV), with each phase testing in larger groups and answering different questions about the treatment.
Meta-Analysis
A statistical method that combines results from multiple independent studies on the same topic to produce a more reliable overall conclusion. Meta-analyses are considered among the highest forms of evidence because they pool data from many studies, reducing the impact of any single study's limitations.
Placebo-Controlled Study
A type of clinical trial where one group receives the actual treatment and another group receives an inactive substance (placebo) that looks identical, so researchers can determine whether observed effects are truly caused by the treatment rather than by expectation or chance.
Preclinical Research
Laboratory and animal studies conducted before a treatment is tested in humans, used to evaluate basic safety, biological activity, and potential side effects. Promising preclinical results are necessary but not sufficient to confirm a treatment will work in people.