Control group

A control group is a comparable set you leave alone, so you can tell whether a change caused a result or everything moved anyway.

In a little more detail

It is what separates a real finding from a coincidence. When a study reports that something worked without one, it has not shown that the something was responsible.

Related terms

Baseline: A baseline is the measurement you take before making changes, so later numbers have something to be compared against.
Variance: Variance is how much a result moves around when you repeat the same test.

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