Study design
Sample size
The number of participants, samples or observations included in a study.
What it means
Definition
Sample size. Sample size affects precision and reliability. Very small studies are more likely to produce unstable estimates, miss important harms or exaggerate apparent benefits.
What it can tell you
It can show how close the evidence is to a real human health outcome.
What it cannot tell you
It cannot prove that a treatment works in people unless human outcome data are available.
Headline trap
Why this matters in headlines
A study of 12 people can be useful early work, but it rarely justifies sweeping public-health claims.