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Confidence Intervals

Confidence Intervals. Quantifying uncertainty. 1. A 95% confidence interval is… A. 95 % sure that the mean is a particular number. B. 95% sure that the sample mean is the population mean C. about 2 standard deviations above and below the mean

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Confidence Intervals

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  1. Confidence Intervals Quantifying uncertainty

  2. 1. A 95% confidence interval is… A. 95 % sure that the mean is a particular number. B. 95% sure that the sample mean is the population mean C. about 2 standard deviations above and below the mean D. 95 % sure that the mean lies between two numbers

  3. 1. If the sample mean is .45 and the standard deviation is .03, then the confidence interval is… A. There is no way to be sure because we can never know the population. B. The confidence interval is 15% - 75%. C. The confidence interval is 39%-51% D. The confidence interval is 42% - 48%.

  4. 1. The margin of error is … A. Question wording. B. estimated standard deviation of the sampling distribution C. When pollsters report the wrong marginals. D. when polls are accurate, they don’t have a margin of error

  5. 1. A 95% confidence interval is … than a 90% confidence interval A. There is no such thing as a 90% confidence interval B. less precise than C. more precise than D. not as good as a 100 % confidence interval

  6. Confidence depends on differences Assume a 3% margin of error. Which candidate is winning? A B

  7. Confidence intervals about relationships Remember the standard normal? Mean = 0, standard deviation is 1 We talk about rejecting the null hypothesis with 95% confidence, or only 90% confidence, or 99.9% confidence

  8. Confidence intervals are partially a function of n

  9. Confidence intervals are also partially a function of the standard deviation of the sample – the higher the variation, the lower the confidence

  10. Null Hypothesis Rejecting the null hypothesis is saying that you tried to prove your hypothesis wrong, but were unable to prove it wrong This does not mean we have proved it with 95% confidence, or proved it at all

  11. The importance of randomness

  12. The importance of randomness

  13. On line polls During the first weekend of the crisis in Japan, CNN.com, on its main page, asked readers the question: "Do you have confidence in U.S. disaster preparedness?" More than 375,000 voted. Eighty percent answered no -- they said they did not have confidence.

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