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# hw4 - BIOST/EPI 513 Spring Quarter 2011 Dr McKnight...

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BIOST / EPI 513 Spring Quarter 2011 Dr. McKnight HOMEWORK 4 Due in the class online drop box at 9pm, Monday, April 25, 2011 Except for the lowess plot requested in problems 2 and 3, please do not turn in any computer output. These problems ask you to use data from the Western Collaborative Group Study (WCGS) found in wcgs.dta and documented in wcgs.codebook.txt on the Assignments page of the class website. 1. Using the WCGS data and logistic regression, examine the evidence for whether systolic blood pressure (SBP) 125 mmHg is associated with the risk of a CHD event (any type) during follow-up. (a) Present a 2 × 2 table of counts, together with appropriate percentages or proportions and confidence intervals as descriptive information. (b) Give an odds ratio for the association of SBP 125 with the risk of a CHD event (any type) during follow up. (c) Give a 95% CI for this odds ratio. (d) Choose an appropriate hypothesis test for whether this odds ratio is one and: i. State your choice and give a short (one sentence) justification for it ii. Give the value of the test statistic iii. Name the reference probability distribution to which you compare it to obtain a P-value iv. Give the P-value for your test v. State your conclusions from the hypothesis test. (e) In one or two sentences, give a summary of the findings of your analysis such as would be appropriate for the results section of a scientific paper reporting these data.

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