What best describes a negative control group?

• A. Group where an effect is expected
• B. The group that receives the treatment
• C. The group is measured to ensure the instrument is working
• D. Group where there should not be an effect

Answer: (D)

In experiments, a negative control provides a baseline where no treatment or intervention that could cause an outcome is applied. The idea is to show what happens due to background variation or artifacts alone, so any real effect seen in the experimental group can be attributed to the treatment rather than other factors. If the negative-control group shows no effect as expected, you can trust that the observed effect in the treated group is due to the treatment. If an effect appears in the negative control, that flags potential issues like contamination or bias.

The other descriptions don’t fit as well: an effect being expected describes a positive control, which is used to confirm that the system can produce a response. The group that receives the treatment is the experimental group, not the negative control. Measuring to ensure the instrument is working describes a calibration or quality-control check, not a negative-control setup.