More dogs are being diagnosed with thyroid problems than have been diagnosed in the past. A researcher identified 50 puppies without thyroid problems and kept records of their diets for several years to see if any developed thyroid problems.

This is a (n)

• randomized experiment

• observational prospective study

• survey

The owner of a car dealership planned to develop strategies to increase sales. He hoped to learn the reasons why many people who visit his car lot do not eventually buy a car from him. For one month he asked his sales staff to keep a list of the names and addresses of everyone who came in to test drive a car. At the end of the month he sent surveys to the people who did not buy the car, asking them why. About one third of them returned the survey, with 44% of those indicating that they found a lower price elsewhere.

Which is true?

i. The population of interest is all potential car buyers.

ii. This survey design suffered from non-response bias.

Check the best answer.

a. Only I

b. neither

c. I and II

d. Only II