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Problem-Solving and Data AnalysisVery hardChoosing the sample that best supports generalisation

Problem-Solving and Data Analysis practice question

A researcher wants to estimate the average time all students at a university spend commuting. Which sample would best support generalising to the whole student body?

  1. A. 500 students selected at random from the university's enrolment recordsCorrect
  2. B. 500 students surveyed in the car park at 8 a.m.
  3. C. 500 students who reply to a poster in the halls of residence
  4. D. The 500 students in the largest lecture course

Answer: A. 500 students selected at random from the university's enrolment records

Random selection from the full list gives every student an equal chance and avoids the biases of the other samples.

Why the other answers are wrong

B. 500 students surveyed in the car park at 8 a.m.
Car-park users drive, and early arrivers may commute far — a biased group.
C. 500 students who reply to a poster in the halls of residence
Hall residents live on campus and commute little; and they self-select.
D. The 500 students in the largest lecture course
One course's students are not representative of all.

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