1. Researchers are studying the absorption of two drugs into the bloodstream. Each drug is to be injected at three dosages. There are 24 people in the study, and they are randomly divided into six groups. Each of the six groups is randomly assigned to a different drug and dosage combination. After 30 minutes the concentration of drugs in a subject's blood is determined. Which of the following is correct?
A. The type of drug is a factor.
B. The dosage of the drug is a factor.
C. Both answers are correct.
2. The administration at a large state university is interested in getting the opinions of students on a proposed instructional fee for use of computer labs on campus. They select a simple random sample of 50 freshmen, 50 sophomores, 50 juniors, and 50 seniors. This is an example of
A. a systematic sample.
B. a stratified random sample.
C. a simple random sample.
3. Two amateur gardeners are interested in comparing the yields of two varieties of tomatoes. They each have small backyard gardens. Each gardener is going to plant three plants of each variety in his garden. The first gardener will select six small areas in his garden for planting, then choose three of these at random for the three plants of the first variety and then use the remaining three for the second variety. The second gardener will follow the same procedure with his own randomization in his garden. At the end of the growing season they will compare the yields of the two varieties. In this example the gardens are
A. a lurking variable.
B. the explanatory variable.
C. blocks.