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Unformatted text preview: Lecture 24 1. Summarizing comparisons of survivor functions from Proc Lifetest 2. Proportional hazards regression: Proc PHreg 3. Graphical checks of proportional hazards assumption 4. Testing whether hazards are proportional 5. Time-varying explanatory variables 1 Summarizing tests comparing survivor functions When a test finds a significant difference between survivor curves, it does not tell us when they differ. Three common approaches to summarizing comparison of two groups A and B : 1. If curves are consistently separated, report overall result. ˆ ˆ If S A is consistently lower than S B , then group A suffered more early events and had a smaller percent surviving at any given time. Report results of log-rank test. During the two years after treatment, the proportion surviving was significantly higher in group B (log-rank test, p = .0378). 2 2. Select a percent surviving, and report times when each group reached it. Common choice is 50% surviving, the median survival time. Group A Percent 75 50 25 Group B 75 50 25 Quartile Estimates Point 95% Confidence Interval Estimate [Lower Upper)...
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