Question

A company wants to compare two washing detergents (Brands A and B) to see which best keeps colors from fading. Twenty new, identical red t-shirts will be used in the trials. Ten t-shirts are washed 15 times with Brand A in warm water. The other 10 t-shirts are washed with Brand B in cold water. The amount of fading is rated on a 0 to 100 scale, and the mean for the t-shirts washed in Brand A is compared to the mean for the others. Is this a good experimental design

Answer 1

No, because water temperature is confounded with brand of detergent.

Explanation:

There is a very possible chance of allowing a third or confounding variable to have creepwd into the research. The aim was to investigate which of two detergents prevents color from fading. Hence, the test for both detergents should be carried out under the same research condition. However, with adoption of different water temperature for each of detergent A and B, there may be a relationship between fading and water temperature which is not what are trying to investigate. This difference in temperature will thus cause a spurious relationship in our research. Hence, water temperature has been confounded with detergent brand, making this experimental design a bad one.