What our evidence ratings mean
How we grade the research behind every guide, from limited to strong.
Every guide on this site shows an evidence rating. It answers one question: how strong is the published research behind what this guide says? We set it from the studies, not from what would sell more.
Strong
Research: strong (what this means)Several well-run studies, ideally randomized controlled trials or a solid review of them, point the same way.
Moderate
Research: moderate (what this means)Controlled studies support it, but they're small, or they measured some outcomes and not others.
Emerging
Research: early (what this means)Early studies look promising, but there aren't enough of them yet to be confident.
Limited
Research: limited (what this means)Only a few small or low-quality studies, or experts disagree. People may still find it helpful, but the research hasn't caught up.
An example
Mouth taping itself is rated limited: a 2025 systematic review found the existing studies were small and low quality. We say that plainly, even though our partner sells mouth tape. Nasal strips for snoring are rated moderate, because controlled trials support them for snoring but not for sleep apnea.