Question

What is wrong with the following experiment?

I am testing the type of shampoo (Pantene, Head & Shoulders, and a generic brand). I have the person with Pantene wash their hair twice a day, the person with Head & Shoulders wash three times a day and the person
with the generic brand wash once a day. I have them use the same amount of shampoo each time the wash, the
same amount of water.

Answer 1

They all must wash their hair the same amount of times and with the same amount of shampoo. Because you want to see the difference when in the hair in the right way. If you have them wash their hair different amount of times then the calculations will be incorect and will be wrong automatically since you didn't start off with the same amount of times washed for all shampoos.