Study design
Control group
The comparison group used to judge what would happen without the tested exposure or intervention.
What it means
Definition
Control group. A control group gives context to the intervention or exposed group. Without it, changes over time may reflect natural recovery, background trends or measurement variation rather than the intervention.
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 before-and-after claim is weaker if there is no comparable control group.