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hw9 - BIOST/EPI 513 Spring Quarter 2011 Dr McKnight...

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BIOST / EPI 513 Spring Quarter 2011 Dr. McKnight HOMEWORK 9 Due in the class online drop box at 9pm, Tuesday, May 31, 2011 Except for the plot requested in question 1, please do not turn in any computer output. 1. This question concerns the treatment comparison in a clinical trial, ACTG019, of Zidovudine (ZDV) vs placebo in HIV + patients. Follow-up data from this trial are available in the file actg019.dta on the Assigments page of the class website. The outcome event of interest is progression of disease, defined as either death or development of frank AIDS. (a) Plot Kaplan-Meier curves for the two treatment groups (ZDV and placebo) on the same set of axes and present the plot in your homework. Which group appears to have the better prognosis? (b) Compare the the two treatment groups using the logrank test. Give test statistic, reference distribution and P-value for this test. What do you conclude? (c) Fit a Cox regression model with a single binary independent variable indicating treatment group to these data. Present the relative risk (hazard ratio) comparing ZDV to placebo and the 95% confidence interval for this relative risk.
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