The quality of evidence tells us how much we can trust it and how much we can rely on it to help us make decisions. Evidence quality can be rated using four levels: high, moderate, borderline, and inconclusive.

• High: When the quality is high, scientists are very confident that the evidence shows the real effects of the treatment or test. There is very little chance that new research will change their confidence. We can really trust the evidence.
• Moderate: When the quality is moderate, scientists are fairly confident that the evidence shows the real effects of the treatment or test. But more research could change this. And it could show different effects of the treatment or test. Still, we can trust this evidence enough to help us make decisions about the treatment or test.
• Borderline: This means that scientists aren't very confident about this evidence. More research is needed. We can't really trust this type of evidence. But if we're careful we may be able to use it to make decisions about the treatment or test.
• Inconclusive: Evidence may be inconclusive when not enough studies have been done or when the results of different studies don't agree. Or it may be that the studies were not done well enough to provide good evidence. We can't really trust this type of evidence. But sometimes it's the only evidence available.