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Logistic Regression and Survival Analysis - Kaplan-Meier (K-M) Estimator - Biostatistical Assignment Help
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Internal Code: 6IJE
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Task: 1 Two groups of rats were exposed to a toxic chemical added to their food and water, in two doses, low and moderate. The survival times (weeks since exposure to death) for these two groups are: Group 0 (low dose): 18, 23, 25, 26, 29*, 30, 30, 31, 31*, 32* Group1 (moderate): 13, 13, 15, 17, 17*, 18, 18, 21, 23, 23*, 24, 25, 25 *starred quantities denote censored observations Source: Woolson R. (1987). Part 1-1 Calculate Kaplan-Meier (K-M) Estimator by creating a table only for the low dose group. You can follow the example like the one at the bottom of page 75 of the course reader. Please do not run SAS for this problem. Make sure to include the following columns: Time, Event, Censored, At Risk, and Cumulative Survival. Part 1-2 Use PROC LIFETEST to create a survival curve for each group. Note: you need to create this data set yourself via the DATA step. Based on the result from PROC LIFETEST, determine the median survival time for each group and provide a 95% confidence interval. Use the log-rank test to compare the survival functions between the low dose group and the moderate group. Write a sentence interpreting the test results. Part 1-3 Write a Cox regression model, which could be used to estimate the hazard ratio comparing rats who receive a moderate dose of a toxic chemical to rats who receive a low dose. Fit the model by using PROC PHREG. Based on the result, give the estimate of the hazard ratio and its 95% confidence interval. Is the toxic chemical associated with death? State your conclusion. Task: 2 A common complication of hospital stays for patients with burn wounds is infection of the wound and death. Inchida et al. (1993) conducted a study to evaluate a change in disinfectant practices in a Midwestern university medical center (Klein & Moeschberger, 1997). Data collected on 154 burn patients can be found in BURN.SAS7BDAT. Part 2-1 Define a Cox model that allows you to test the hypothesis that the rate of times to infection is the same in the two bathing solution groups after adjusting for the SEX variable. Based on the result, give the estimate of the hazard ratio and its 95% confidence interval for the bathing solution (using the standard method as the baseline) and state your conclusion. Variables:- INFECTTIME: time to infection
- INFECTEVENT: 0 indicates the censored observations
- BATHSOL: 1 - new cleansing protocol; 0 - standard solution
- SEX: 1 - female; 0 - male
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