Suppose that you have developed three new kinds

Question

of hair shampoo, and you want to know how people's preference depends on their
age. Design an experiment to find out.

Answer 1

You might have people randomly assigned to the three shampoos and block by age.

Shampoo A B C

age group 1

age group 2

age group 3

Give each age group shampoos A, B, C. have them use each shampoo for a week and then rate them.