Which statement about controls is NOT true in an experimental setup?

• A. A negative result with a positive control is required to validate the test
• B. With a negative control, a negative result is expected
• C. With a positive control, a positive result is expected
• D. A positive result with a negative control could indicate contamination

Answer: (A)

In an experimental setup, controls show whether the procedure itself is producing effects or if any observed results come from the treatment being tested. A negative control should yield no effect, confirming there’s no unintended activity. A positive control should yield the expected effect, proving the assay can detect it when it’s present. If you get a positive result with a negative control, that suggests contamination or a non-specific signal, which undermines the reliability of the test. The statement that a negative result with a positive control is required to validate the test is not true, because the positive control should produce a positive result to confirm the assay works; a negative result there would indicate the test isn’t functioning properly.