What best describes a positive control group?

• A. Group where no effect is expected
• B. A separate control with a placebo
• C. A group used to check that the experimental setup can produce a known effect
• D. Group where an effect is expected

Answer: (D)

A positive control group is used to show that the experimental system is capable of producing a known, detectable effect. This validates that the assay or procedure is working as intended. If the positive control yields the expected result, you can interpret the results from the experimental group with more confidence; if it doesn’t, something about the setup or reagents may be faulty, making the experimental results unreliable.

For example, in a test of a new drug’s effect on lowering blood pressure, a positive control might receive a standard antihypertensive drug that reliably lowers blood pressure. If this group shows the expected effect, you know the measurement and setup can detect a real change. Then, if the new drug group shows no effect, you can attribute that to the drug’s lack of efficacy rather than a flawed assay.

Contrast this with a negative control, where no effect is expected, to ensure that any observed changes are due to the treatment and not other factors.