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Math·Problem-Solving and Data Analysis·Evaluating statistical claims: Observational studies and experiments
hard
For a study, a group of gophers will be selected from a habitat consisting of gophers, and a group of groundhogs will be selected from a habitat consisting of 200 groundhogs. Some of the gophers and groundhogs will be in a treatment group, and some of the gophers and groundhogs will be in a control group. Which of the following is necessary for this study to attempt to establish a cause-and-effect relationship between two variables?
A
The number of gophers in the treatment group is equal to the number of groundhogs in the treatment group, and the number of gophers in the control group is equal to the number of groundhogs in the control group.
B
The gophers and the groundhogs are randomly selected from their respective habitats.
C
The gophers and the groundhogs are randomly assigned to the treatment and control groups.
D
The average age of the gophers in the treatment group is equal to the average age of the groundhogs in the treatment group, and the average age of the gophers in the control group is equal to the average age of the groundhogs in the control group.