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[英]probability of survival at particular time points using randomForestSRC
[英]Comparing survival at specific time points
我有以下生存數據
library(survival)
data(pbc)
#model to be plotted and analyzed, convert time to years
fit <- survfit(Surv(time/365.25, status) ~ edema, data = pbc)
#visualize overall survival Kaplan-Meier curve
plot(fit)
這是生成的 Kaplan-Meier 圖的樣子
我正在以這種方式進一步計算 1、2、3 年的生存率:
> summary(fit,times=c(1,2,3))
Call: survfit(formula = Surv(time/365.25, status) ~ edema, data = pbc)
232 observations deleted due to missingness
edema=0
time n.risk n.event survival std.err lower 95% CI upper 95% CI
1 126 12 0.913 0.0240 0.867 0.961
2 112 12 0.825 0.0325 0.764 0.891
3 80 26 0.627 0.0420 0.550 0.714
edema=0.5
time n.risk n.event survival std.err lower 95% CI upper 95% CI
1 22 7 0.759 0.0795 0.618 0.932
2 17 5 0.586 0.0915 0.432 0.796
3 11 4 0.448 0.0923 0.299 0.671
edema=1
time n.risk n.event survival std.err lower 95% CI upper 95% CI
1 8 11 0.421 0.1133 0.2485 0.713
2 5 3 0.263 0.1010 0.1240 0.558
3 3 2 0.158 0.0837 0.0559 0.446
如您所見,結果輸出顯示了不同edema
水平之間的 95% 置信區間,但沒有實際的 p 值。 無論置信區間是否重疊,我仍然很清楚這些時間點的生存率是否有顯着差異,但我想要准確的 p 值。 我該怎么做?
我認為以下代碼可以滿足您的需求:
library(survival)
data(pbc)
#model to be plotted and analyzed, convert time to years
fit <- survfit(Surv(time/365.25, status) ~ edema, data = pbc)
#visualize overall survival Kaplan-Meier curve
plot(fit)
threeYr <- summary(fit,times=3)
#difference in survival at 3 years between edema=0 and edemo=1 (for example) is
threeYr$surv[1] - threeYr$surv[3]
#the standard error of this is
diffSE <- sqrt(threeYr$std.err[3]^2 + threeYr$std.err[1]^2)
#a 95% CI for the diff is
threeYr$surv[1] - threeYr$surv[3] - 1.96 *diffSE
threeYr$surv[1] - threeYr$surv[3] + 1.96 *diffSE
#a z-test test statistic is
zStat <- (threeYr$surv[1] - threeYr$surv[3])/diffSE
#and a two-sided p-value testing that the diff. is 0 is
2*pnorm(abs(zStat), lower.tail=FALSE)
或者,可以通過基於估計的概率估計風險比或優勢比來進行比較,並在對數風險比或對數優勢比量表上執行推理/測試。 一般來說,我希望這會表現得更好(在測試規模和置信區間覆蓋率方面),因為在這些尺度上的正態近似比在風險差異尺度上更好。
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