A dog food company wishes to test a new high-protein formula for puppy food to determine whether it promotes faster weight gain than the existing formula for that puppy food. Puppies participating in an experiment will be weighed at weaning (when they begin to eat puppy food) and will be weighed at one-month intervals for one year. In designing this experiment, the investigators wish to reduce the variability due to natural differences in puppy growth rates. Which of the following strategies is most appropriate for accomplishing this?
A) Block on dog breed and randomly assign puppies to existing and new formula groups within each
breed.
B) Block on geographic location and randomly assign puppies to existing and new formula groups
within each geographic area.
C) Stratify on dog breed and randomly sample puppies within each breed. Then assign puppies by
breed to either the existing or the new formula.
D) Stratify on geographic location of the puppies and randomly sample puppies within each
geographic area. Then assign puppies by geographic area to either the existing or the new formula
E) Stratify on gender and randomly sample puppies within gender groups. Then assign puppies by
gender to either the existing or the new formula.