A student wants to determine how his classmates feel about school. He does a survey away from school so all participants will be willing to answer freely. In several cases, younger siblings of his classmates are present, so he lets them take the survey too. He surveys a total of 50 students. Has he done a well-designed, controlled experiment? Select the correct answer.

No. A controlled experiment requires the researcher to manipulate an independent variable and control the conditions. Here, the student only surveys people; he does not manipulate or control an independent variable. Including younger siblings also means the participants may not all belong to the group he wants to study—his classmates. The correct choice is D, “No. His independent variable is not controlled.”

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