Common Core: S-IC.3
Problem 17 of 45s12-017
A city mails a survey on a new bus line to 2,000 homes chosen at random from a full address list. Only 300 reply, mostly daily riders, who tend to favour the line. What bias results?
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Solution walkthrough1:54
- The 2,000 homes were drawn at random from a full list, so every home could be chosen. Choosing is not the problem.
- Only 300 of the 2,000 chosen homes replied, and the people who replied are mostly daily bus riders.
- Chosen people who do not reply, and differ from those who do: that is nonresponse bias.
- Riders are a bigger share of the replies than of the homes, and they favour the line: support looks too high.
- Undercoverage: some cannot be chosen. Voluntary: people pick themselves. Response bias: wording pushes answers.
- Traps: the list was complete (not undercoverage), the city chose the homes (not voluntary), support is too high.