What is the purpose of a negative control?

• A. To confirm that observed effects are caused by the treatment rather than random variation.
• B. To demonstrate the effect of the treatment in the absence of any test substance.
• C. To measure the baseline levels without any treatment.
• D. To provide a secondary measure of interest.

Answer: (A)

The main concept is using a negative control to ensure that any observed change comes from the treatment itself, not random variation or other factors. In a negative control, everything is kept the same as in the treated samples except that the treatment is omitted (or replaced with a neutral substance). If the negative control shows no effect, you can attribute any change seen in the treated group to the treatment rather than chance, contamination, or procedural errors. Negative controls also help detect issues like accidental contamination or unintended influences in the setup. This aligns with the idea of confirming that observed effects are caused by the treatment rather than random variation.