r - 为什么 confint() 结果每次都改变？

Question

当我运行 GEE 时，我使用 glht() 进行事后测试，之后，我使用 confint() 来获得 95%CI 的值。但奇怪的是，当我一次又一次地运行代码时，结果每次都会改变。为什么？

library(multcomp)
library(geepack)
data(dietox)
#dietox$Weight = as.integer(dietox$Weight)
dietox$Cu <- as.factor(dietox$Cu)
mf <- formula(Weight ~ Cu + Time + I(Time^2) + I(Time^3))
gee1 <- geeglm(mf, data=dietox, id=Pig, corstr="ar1")
CI <- glht(gee1,mcp("Cu" = "Tukey"))
confint(CI)


result:
                   Estimate lwr     upr    
Cu035 - Cu000 == 0 -0.4467  -3.7996  2.9061
Cu175 - Cu000 == 0  1.1821  -2.9923  5.3565
Cu175 - Cu035 == 0  1.6288  -2.6616  5.9193

run the code again:
                   Estimate lwr     upr    
Cu035 - Cu000 == 0 -0.4467  -3.8002  2.9067
Cu175 - Cu000 == 0  1.1821  -2.9931  5.3573
Cu175 - Cu035 == 0  1.6288  -2.6624  5.9201

again:
                   Estimate lwr     upr    
Cu035 - Cu000 == 0 -0.4467  -3.7985  2.9050
Cu175 - Cu000 == 0  1.1821  -2.9910  5.3552
Cu175 - Cu035 == 0  1.6288  -2.6603  5.9179
.......

标签： r