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Problem-Solving and Data AnalysisEasy–MediumWhich sampling method gives an unbiased estimate

Problem-Solving and Data Analysis practice question

A city wants to estimate the proportion of its residents who own a car. Which sampling method is most likely to produce an unbiased estimate?

  1. A. Selecting 500 residents at random from the city's electoral roll and contacting each of them.Correct
  2. B. Surveying 500 drivers at a petrol station.
  3. C. Surveying 500 passengers at the main bus station.
  4. D. Posting a poll on the city's car club website.

Answer: A. Selecting 500 residents at random from the city's electoral roll and contacting each of them.

A random selection from a list of all residents gives every resident an equal chance of inclusion.

Why the other answers are wrong

B. Surveying 500 drivers at a petrol station.
Petrol-station customers nearly all own cars.
C. Surveying 500 passengers at the main bus station.
Bus passengers are less likely than average to own cars.
D. Posting a poll on the city's car club website.
Car-club members own cars by definition.

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