negative control

Meaning: In an experiment, the negative control is the comparison condition where the independent variable is absent or inactive. It sets the baseline. A no-treatment group controls for the passage of time, maturation, outside events and regression to the mean. A placebo group also controls for expectation, since participants believe they may be receiving treatment. Any difference between the experimental group and the negative control can then be attributed more confidently to the independent variable. Random assignment helps make the groups equivalent at the start.

On the MCAT: A passage describes a study, for example a mindfulness program and anxiety scores, and asks you to identify the control group, explain why it is included, or interpret results. The negative control should show little or no change in the dependent variable. If its scores improve as much as the treatment group's, the improvement cannot be credited to the program. Likely explanations are a placebo effect, history, or another confound. Questions may also ask how to improve a design that lacks a control group.

Common confusion: "Negative" does not mean a bad outcome or a harmful treatment. It means the expected result is no effect. It is also not the same as a positive control, which is a condition known to produce the effect and shows the measure can detect it. Controlled variables, which are held constant across all groups, are different again.