A middle school contains sixth, seventh, and eighth graders. Each grade level contains approximately the same number of students. The principal wants to find the answer to a survey question affecting each student in the school. He asks a sample group “What time do you get up in the morning?” Which of these characteristics define the best sample?

Because the three grade levels have approximately the same number of students, the sample should include an equal number chosen at random from each grade. Random selection helps make the sample representative and avoids favoring students with a particular arrival routine. Choice B, an equal number of students chosen at random from each grade level, best meets both goals; the first students to arrive or students on one bus may be unrepresentative.

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