Problem-Solving and Data AnalysisEasyRecognising a biased sample in an advert
Problem-Solving and Data Analysis practice question
An advert says '9 out of 10 dentists recommend our toothpaste.' The 10 dentists asked all work for the company that makes the toothpaste. What is the main problem with the claim?
- A. The dentists asked are not a fair sample; they have a reason to favour the company.Correct
- B. Ten is an odd number of dentists.
- C. Dentists know nothing about toothpaste.
- D. The advert should say 90%.
Answer: A. The dentists asked are not a fair sample; they have a reason to favour the company.
People with a stake in the answer are not a fair sample.
Why the other answers are wrong
- B. Ten is an odd number of dentists.
- The number's parity is irrelevant.
- C. Dentists know nothing about toothpaste.
- Dentists are experts; the problem is who was asked.
- D. The advert should say 90%.
- 9 out of 10 and 90% mean the same.
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