Question

As dogs age, diminished joint and hip health may lead to joint pain and thus reduce
a dog’s activity level. Such a reduction in activity can lead to other health concerns
such as weight gain and lethargy due to lack of exercise. A study is to be conducted to
see which of two dietary supplements, glucosamine or chondroitin, is more effective in
promoting joint and hip health and reducing the onset of canine osteoarthritis.
Researchers will randomly select a total of 300 dogs from ten different large veterinary
practices around the country. All of the dogs are more than 6 years old, and their
owners have given consent to participate in the study. Changes in joint and hip health
will be evaluated after 6 months of treatment.
(a) What would be an advantage to adding a control group in the design of this study?

(b) Assuming a control group is added to the other two groups in the study, explain how
you would assign the 300 dogs to these three groups and make a diagram for a
completely randomized design.

(c) Rather than using a completely randomized design, one group of researchers
proposes blocking on clinics, and another group of researchers proposes blocking on
breed of dog. How would you decide which one of these two variables to use as a
blocking variable?

(d) Suppose there are 100 small size bread dogs, 120 medium size bread dogs and 80
big bread dogs. Make a diagram for a randomize block design according to bread size.

Answer 1