Evidence

Information or data on which a medical decision or guidance is based, collected through systematic and controlled research.

Important characteristics:

Based on research
Evidence comes from observations, experiments, surveys or other forms of structured research.

Objective and repeatable
Research must be conducted in such a way that others can repeat it and arrive at similar results.

Based on the scientific method
This involves formulating a hypothesis, testing it, analysing it and drawing conclusions based on the data.

Peer-reviewed
Reliable scientific evidence is often published in professional journals that undergo a peer review process.

Hierarchy of evidence
Some types of evidence are considered stronger than others. For example:

Strong evidence: Systematic reviews, meta-analyses, randomised controlled trials (RCT).
Weaker evidence: Case reports, observations, expert opinions.