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Homework Help: AP Statistics MCQ

  1. Dec 3, 2015 #1
    1. The problem statement, all variables and given/known data
    One month the actual unemployment rate in France was 13.4%. If during that month you took a SRS of 100 Frenchmen and constructed a confidence interval estimate of the unemployment rate, which of the following would have been true?

    A) The center of the interval was 13.4.
    B) The interval contained 13.4.
    C) A 99% confidence interval estimate contained 13.4.
    D) The z-score of 13.4 was between +-2.576.
    E) None of the above are true statements.

    2. Relevant equations

    3. The attempt at a solution
    Since (unemployed, not unemployed) are 2 variables, I think the confidence interval for a proportion applies here. Since np = 13.4 > 10 and n(1-p) = 100 - 13.4 > 10, a normal distribution can be used to approximate the binomial distribution. Then shouldn't A, B, C, and D all be correct? It is a simple random sample, and the sample size is less than 10% of the French population. But the answer key says the exact opposite; E is the correct answer. Could somebody explain why? Thanks! :)
  2. jcsd
  3. Dec 3, 2015 #2

    Ray Vickson

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    Science Advisor
    Homework Helper

    Basically: in a random sample, the observed unemployment rate could vary from 0% to 100%. That is unlikely, but rare things DO happen. Even a 99% confidence interval could miss the 13.4% figure, because 99% confidence intervals will contain the true mean 99% of the time. That means they will fail to contain the true mean 1% of the time, and this could be one such time.
  4. Dec 4, 2015 #3
    Ah I see... Thanks! :)
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