A veterinarian knows that the supplement glucosamine is beneficial for dogs’ joints. He wants to determine if a supplement with both glucosamine and chondroitin would be more beneficial than glucosamine alone for dogs’ joint health. The veterinarian asks the owners of dogs with known joint issues if they would be willing to have their dog participate in his study, and 32 owners agree to the study. Sixteen dogs are randomly assigned to the glucosamine group and the remaining 16 are assigned to the glucosamine with chondroitin group. After 6 months, the dogs’ joint health is measured for each treatment and compared. The results of the study were inconclusive and the veterinarian decides to do the experiment again. He gets 24 volunteers and decides that he needs to use a randomized block design. Which variable would not be an appropriate variable for blocking?

age
size
color of coat
breed