Evidence
Evidence is data or observations that support or contradict a scientific claim, gathered and evaluated through investigation.
Definition
Evidence is information from observations or experiments that helps you decide whether an idea is right; it is what you point to when someone asks "how do you know?". In a scientific argument, a claim is supported by evidence and by reasoning that explains why the evidence supports the claim, and evidence can support a hypothesis or contradict it, with both kinds valuable. Its weight depends on the quality of the method (controls, sample size, calibration), on whether it comes from independent sources, and on whether it could have been produced if the claim were false. The strongest evidence is that which was predicted in advance and could have falsified the claim.
Example
The evidence that sunlight helps plants grow is the data: window plants averaged $9\ \text{cm}$ and closet plants $5\ \text{cm}$ after two weeks. For the claim that warmer water dissolves salt faster, the evidence is mean times of $48$, $26$, and $14\ \text{s}$ at $10^\circ\text{C}$, $30^\circ\text{C}$, and $50^\circ\text{C}$ with ranges of only $2$ to $5\ \text{s}$, and the reasoning is that differences between temperatures far exceed variation within each. Twenty rock samples whose mass-to-volume ratios cluster at $2.7\ \text{g/cm}^3$ are evidence that they are one material, strengthened by the small scatter, by a line through the origin, and by the absence of the spread that a mix of materials would have produced.
Key Insight
Evidence is not an opinion or a feeling; "I think so" is not evidence, while "I measured it three times" is. Data become evidence only when linked to a claim, so the same numbers can be strong evidence for one claim and no evidence at all for another. Absence of evidence is weak evidence of absence only when the experiment could have detected the effect; a null result from an insensitive method proves nothing either way.