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A professor wanted to know whether a prep course would increase students’ test scores.

Twelve subjects were randomly chosen to take the prep course, and they scored an average of $20.3$ with a standard deviation of $8.3\text{ points}$. Another $12\text{ subjects}$ were randomly chosen who were not allowed to take the test prep course, and they scored an average of $18.3$ with a standard deviation of $9.1\text{ points}$.

Despite these scores, why might the professor not be convinced that the course helps?

A

A difference of $2\text{ points}$ on the test is not practically significant.

B

The variability is such that the higher scores achieved by the group who took the prep course could have been a result of chance.

C

Randomization was not properly used in this situation.

D

A control group was not properly used in this situation.

E

Bias was obvious in the measurement of the students’ test scores.

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