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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.
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
25 Group B 75
25 Quartile Estimates
95% Confidence Interval
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- Fall '11