You wanted to see if Drug A or Drug B was better at treating dandruff. You were concerned that your results might be influenced by hair color and set up the study as a randomized block design where people with same hair color were put together to create a block. If there were 30 people in the study, what was the degrees of freedom for the statistical test?

I said 15 pairs, so df is 15-1 = 14.

Please check my answer. Thank you.