Glossary
Level of evidence.
Direct answer
The level of evidence ranks scientific findings by how well the underlying study design rules out chance and systematic error. A single observation sits low, a randomised controlled trial sits high, and a careful systematic review sits higher still. The level judges how a study was built, not whether its result is true.
A high level does not mean a result is correct: it means the design excludes known sources of error more effectively. A poorly conducted randomised trial can be weaker than a rigorous observational study. Reading an evidence scale therefore means checking how the work was carried out, not only the label attached to it.
In equine medicine the available evidence sits lower on average than in human medicine: group sizes are small, trials are expensive, and comparison arms are delicate when the animals are valuable. Many recommendations rest on case series or on transfer from other species. That is no reason for distrust, but every reason to state the level openly.
Randomised controlled trialSystematic reviewExternal validity
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.