Comm 291 Statistics T-Stats Means 2014 Assignment 4 Berkowitz

# Comm 291 Statistics T-Stats Means 2014 Assignment 4 Berkowitz

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Question 1 – Foundations of Inference a) A survey of 200 employees finds that 48% have received this year’s flu vaccine. An approximate 95% confidence interval is (0.409,0.551). i. How would the confidence interval change if the sample size had been 800 instead of 200? CI = (0.445, 0.515) ii. How would the confidence interval change if the confidence level had been 90% instead of 95%? CI = (0.442, 0.538) iii. How would the confidence interval change if the confidence level had been 99% instead of 95%? CI = (0.389, 0.571) b) Which of the following are true? If false, explain briefly. i. A very low P-value provides evidence against the null hypothesis. True. ii. A high P-value is strong evidence in favour of the null hypothesis. True. iii. A P-value above 0.10 shows that the null hypothesis is true. False. It is true only when Alpha is less than 0.10. iv. If the null hypothesis is true, you can’t get a P-value being 0.01. False. You can still get a P-value of 0.01 when the null hypothesis is true if you set alpha to be less than 0.01. c) A change is made that should improve student satisfaction with the way grades are processed. The null hypothesis, that there is an improvement, is tested versus the alternative, that there is no change. Do you think this statement is correct? Explain in one or two sentences. No, the statement is incorrect because the null hypothesis represents no change from the current position. The statement should reverse the two hypotheses with the null hypothesis being “that there is no change” and the alternative hypothesis being “that there is an improvement.”
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• Spring '10
• E.Fowler
• Null hypothesis, Statistical hypothesis testing, Montreal

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