更新模型：未删除三向交互项答案

【问题标题】：Update model : 3-way interaction terms not dropped更新模型：未删除三向交互项
【发布时间】：2018-07-24 19:51:48
【问题描述】：

我的问题与这个高度相关： R update() interaction term not dropped

但是，我的预测变量中没有多个类别，因此我不明白我的问题与答案有何关系。可能是我没看懂……

我想在模型缩减过程中一次删除一个无关紧要的三向交互项。

但是，会发生以下情况：

model1 <- lme(sum.leafmass ~ stand.td.Sept.2017*stand.wtd.Sept.2017*I((stand.td.Sept.2017)^2)*I((stand.wtd.Sept.2017)^2), random = ~1|block/fence, method="ML", data=subset(Total.CiPEHR, species=="EV"), na.action=na.omit)

model2 <- update(model1,.~.-stand.td.Sept.2017:stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2))
summary(model2)   ##works correctly to eliminate insignificant 4-way interactions

summary(model2)
                                                                         DF   t-value p-value
(Intercept)                                                               4  3.849259  0.0183
stand.td.Sept.2017                                                        4 -1.436666  0.2242
stand.wtd.Sept.2017                                                       4 -2.921806  0.0432
I((stand.td.Sept.2017)^2)                                                 4  4.594303  0.0101
I((stand.wtd.Sept.2017)^2)                                                4 -0.313197  0.7698
stand.td.Sept.2017:stand.wtd.Sept.2017                                    4 -1.301935  0.2629
stand.td.Sept.2017:I((stand.td.Sept.2017)^2)                              4  1.853451  0.1374
stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2)                             4  4.354757  0.0121
stand.td.Sept.2017:I((stand.wtd.Sept.2017)^2)                             4 -0.028199  0.9789
stand.wtd.Sept.2017:I((stand.wtd.Sept.2017)^2)                            4  1.598564  0.1852
I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2)                      4 -1.683214  0.1676
stand.td.Sept.2017:stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2)          4  1.972616  0.1198
stand.td.Sept.2017:stand.wtd.Sept.2017:I((stand.wtd.Sept.2017)^2)         4 -1.635314  0.1773
stand.td.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2)   4  2.190518  0.0936
stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2)  4 -0.968249  0.3877

##attempt to remove insignificant 3-way interaction
model3 <- update(model2,.~.,-stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2))
summary(model3)
                                                                         DF   t-value p-value
(Intercept)                                                               4  3.849259  0.0183
stand.td.Sept.2017                                                        4 -1.436666  0.2242
stand.wtd.Sept.2017                                                       4 -2.921806  0.0432
I((stand.td.Sept.2017)^2)                                                 4  4.594303  0.0101
I((stand.wtd.Sept.2017)^2)                                                4 -0.313197  0.7698
stand.td.Sept.2017:stand.wtd.Sept.2017                                    4 -1.301935  0.2629
stand.td.Sept.2017:I((stand.td.Sept.2017)^2)                              4  1.853451  0.1374
stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2)                             4  4.354757  0.0121
stand.td.Sept.2017:I((stand.wtd.Sept.2017)^2)                             4 -0.028199  0.9789
stand.wtd.Sept.2017:I((stand.wtd.Sept.2017)^2)                            4  1.598564  0.1852
I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2)                      4 -1.683214  0.1676
stand.td.Sept.2017:stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2)          4  1.972616  0.1198
stand.td.Sept.2017:stand.wtd.Sept.2017:I((stand.wtd.Sept.2017)^2)         4 -1.635314  0.1773
stand.td.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2)   4  2.190518  0.0936
stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2)  4 -0.968249  0.3877

##3-way interaction term still there.

为什么交互项不会下降？预测变量是连续的，因此应该相互独立，对吧..？

如果我不了解这里的基本内容，请解释一下...

【问题讨论】：

标签： nlme

【解决方案1】：

解决了我自己的问题。

虚拟语法错误。（在 .~. 部分的逗号不正确）

###Incorrect syntax.
model3 <- update(model2,.~.,-stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2))

###Correct syntax.
model3 <- update(model2,.~.-stand.wtd.Sept.2017:I((stand.td.Sept.2017)^2):I((stand.wtd.Sept.2017)^2))

【讨论】：