Question

Aw, rats! A nutrition experimenter intends to compare the weight gain of newly weaned male rats fed Diet A with that of rats fed Diet B. To do this, she will feed each diet to 10 rats. She has available $10$rats from one litter and $10$rats from a second litter. Rats in the first litter appear to be slightly healthier.

(a) If the $10$rats from Litter 1 were fed Diet A, the effects of genetics and diet would be confounded, and the experiment would be biased in favor of Diet A. Explain this statement carefully.

(b) Describe a better design for this experiment.

Short answer

(a) If rats from one litter are fed diet $A$and they gained more weight, it would be difficult to conclude if it is due to genetic health or diet.

(b) Randomized block design would be better.

Step-by-step solution

Given Information

A nutrition expert wants to compare the weight gain of male rats fed with diet A with those fed with diet B. There are ten rats in one litter and ten in other. Rats is first litter are healthier.

To explain the statement.

It means that if ten rats from litter $1$were given diet A, it would be confounded if it is genetic or diet that gave such results. Experiment would be biased toward Diet A.

To implement better design for experiment.

Randomized block design should be used with litter as blocks. Randomly assign half of the rats with diet A and other half to receive diet B. This will allow us to spot the differences in weight gain caused by difference in initial health and genetics.