A researcher numbers each household in the city and uses a random number generator to select individual households for the sample. By chance, none of the households chosen were households of single millennials. This is an example of Answer

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A company's receipts gives a website where customers can fill out a survey to receive a coupon. This is an example of Answer

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Your friend forgot she was supposed to conduct a poll of your high schools' students. She asks everyone in your homeroom if they think the school should have a new mascot. She presents the results to the student council. This is an example of Answer
undercoverage bias