A cosmetics company decides to compare its new nail polish product, Bella, with three other nail polish brands: Primrose, Shine, and Glo. In an experiment, participants are divided into four groups. Each group of women is asked to wear nail polish from one of the four brands. The results for Primrose, Shine, and Glo are compared with those for Bella, and a conclusion is drawn. What does the type of nail polish represent in this case?

Question