A shampoo advertized in your favorite magazine claims to have a secret ingredient that will make your hair thicker and shinier how could you test the claim?

Test the shampoo on different subjects with different hair types (Ex thick, thin) Keep the variables the same for each subject using constants, independent, and dependent variables to test the claim. See if there is any difference in the girls who used the shampoo with the secret ingredient Vs girls who used a regular shampoo with out that ingredient.