﻿# PRACTICAL EXERCISE 2 # ==================== # Read data: path="http://www.uio.no/studier/emner/matnat/math/STK4080/h14/melanoma.txt" melanoma=read.table(path,header=T) # The survival library must be loaded # Kaplan-Meier estimates and summary for for all patients: fit.mel0=survfit(Surv(lifetime,status==1)~1,data=melanoma,conf.type="plain") plot(fit.mel0, mark.time=F, xlab="Years after operation") summary(fit.mel0) # Question a # ---------- # We compute Kaplan-Meier estimates for females and males with standard confidence intervals: fit.sex=survfit(Surv(lifetime,status==1)~sex,data=melanoma,conf.type="plain") # We then make a plot of the estimates: plot(fit.sex, mark.time=F, xlab="Years after operation",lty=1:2) legend("bottomleft",c("females","males"),lty=1:2) # We may use the summary command to obtain the estimated survival with confidence intervals summary(fit.sex) # From the summary we may read of an estimate for the lower quartile # with confidence limits, cf. section 3.2.3 and exercise 3.8 in the ABG-book. # For females the lower quartile becomes 8.33 years with 95% confidence limits # from 5.30 years and upwards (no upper limit can be obtained) # For males the lower quartile becomes 3.36 years with 95% confidence limits from 2.17 to 5.76 years. # We may also obtain the lower quartile with confidence limits from the command: quantile(fit.sex,probs=0.25) # Questions b and c # The commands are as for question a, but using "ulcer" and "grthick" # instead of "sex" when computing the Kaplan-Meier estimates