How should one interpret scientific claims? Here are the headings to an excellent article featured in Nature:

Differences and chance cause variation.
No measurement is exact.
Bias is rife.
Bigger is usually better for sample size.
Correlation does not imply causation.
Regression to the mean can mislead.
Extrapolating beyond the data is risky.
Beware the base-rate fallacy.
Controls are important.
Randomization avoids bias.
Seek replication, not pseudoreplication.
Scientists are human.
Significance is significant.
Separate no effect from non-significance.
Effect size matters.
Study relevance limits generalizations.
Feelings influence risk perception.
Dependencies change the risks.
Data can be dredged or cherry picked.
Extreme measurements may mislead.