Control group

The control group shows what happens without the treatment, so any extra change in the treatment group can be linked to the treatment itself. It might receive nothing, a standard existing treatment, or a placebo, depending on what makes a fair comparison. For example, to test a new fertilizer you grow one set of plants with it and a control set under identical conditions without it. Comparing the two groups isolates the fertilizer's effect from sunlight, water, and soil, which act on both groups equally.