I am confuse by the results of the weights option for coxph. I replicated each row three times from the help page for coxph in the data frame test_freq. I had expected that the coefficients, significance tests, and tests of non-proportionality would yield the same results for the replicated and non-replicated data, but the output below shows differences in all three metrics. Is this the result of a curved response variable? This is likely more of a conceptual question than a language question, but all help is sincerely appreciated.
Mike > test1 $time [1] 4 3 1 1 2 2 3 $status [1] 1 NA 1 0 1 1 0 $x [1] 0 2 1 1 1 0 0 $sex [1] 0 0 0 0 1 1 1 $wt [1] 3 3 3 3 3 3 3 > test_freq time status x sex 1 4 1 0 0 2 4 1 0 0 3 4 1 0 0 4 3 NA 2 0 5 3 NA 2 0 6 3 NA 2 0 7 1 1 1 0 8 1 1 1 0 9 1 1 1 0 10 1 0 1 0 11 1 0 1 0 12 1 0 1 0 13 2 1 1 1 14 2 1 1 1 15 2 1 1 1 16 2 1 0 1 17 2 1 0 1 18 2 1 0 1 19 3 0 0 1 20 3 0 0 1 21 3 0 0 1 > t1 <- coxph( Surv(time, status) ~ x + strata(sex), data=test1, weights=wt) > summary(t1) Call: coxph(formula = Surv(time, status) ~ x + strata(sex), data = test1, weights = wt) n=6 (1 observation deleted due to missingness) coef exp(coef) se(coef) z p x 1.17 3.22 0.744 1.57 0.12 exp(coef) exp(-coef) lower .95 upper .95 x 3.22 0.311 0.749 13.8 Rsquare= 0.353 (max possible= 0.999 ) Likelihood ratio test= 2.61 on 1 df, p=0.106 Wald test = 2.47 on 1 df, p=0.116 Score (logrank) test = 2.67 on 1 df, p=0.102 > cox.zph(t1) rho chisq p x -0.0716 0.00598 0.938 > t_freq <- coxph( Surv(time, status) ~ x + strata(sex), data=test_freq) > summary(t_freq) Call: coxph(formula = Surv(time, status) ~ x + strata(sex), data = test_freq) n=18 (3 observations deleted due to missingness) coef exp(coef) se(coef) z p x 1.41 4.09 0.756 1.86 0.063 exp(coef) exp(-coef) lower .95 upper .95 x 4.09 0.245 0.929 18.0 Rsquare= 0.185 (max possible= 0.879 ) Likelihood ratio test= 3.69 on 1 df, p=0.0549 Wald test = 3.47 on 1 df, p=0.0626 Score (logrank) test = 3.84 on 1 df, p=0.0499 > cox.zph(t_freq) rho chisq p x -0.0697 0.0526 0.819 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.