LME模型加入wait变量后出现Singularity in backsolve报错求助

问题背景 #

我在R里构建线性混合效应模型（LME）时卡壳了：不带wait变量的模型跑得顺顺当当，但一加上四因素交互项Adhesive*Approach*Aging*wait，执行下面的代码就报错：

LME_01 <- lme(
  data_mTBS ~ Adhesive*Approach*Aging*wait,
  na.action = na.exclude,
  data = Data,
  random = ~ 1|data_name
);

报错信息如下：

Error in MEEM(object, conLin, control$niterEM) : Singularity in backsolve at level 0, block 1

数据概况 #

我的数据集有972条观测，7个变量，具体结构如下：

str(Data)
# 'data.frame': 972 obs. of  7 variables:
#  $ data_mTBS : num  20.3 22.7 0 47.8 58.7 ...
#  $ data_tooth: num  1 1 1 1 1 1 1 1 1 1 ...
#  $ Adhesive  : Factor w/ 4 levels "C-SE2","C-UBq",..: 2 2 2 2 2 2 2 2 2 2 ...
#  $ Approach  : Factor w/ 2 levels "ER","SE": 1 1 1 1 1 1 1 1 1 1 ...
#  $ Aging     : Factor w/ 2 levels "1w","6m": 1 1 1 1 1 1 2 2 2 2 ...
#  $ data_name : Factor w/ 40 levels "C-SE2-1","C-SE2-10",..: 11 11 11 11 11 11 11 11 11 11 ...
#  $ wait      : Factor w/ 2 levels "no","yes": 1 1 1 1 1 1 1 1 1 1 ...

数据集前6行的示例：

head(Data)
#   data_mTBS data_tooth Adhesive Approach Aging data_name wait
# 1     20.27          1    C-UBq       ER    1w   C-UBq-1   no
# 2     22.73          1    C-UBq       ER    1w   C-UBq-1   no
# 3      0.00          1    C-UBq       ER    1w   C-UBq-1   no
# 4     47.79          1    C-UBq       ER    1w   C-UBq-1   no
# 5     58.73          1    C-UBq       ER    1w   C-UBq-1   no
# 6     57.02          1    C-UBq       ER    1w   C-UBq-1   no

待推进的对比分析 #

原本我打算模型拟合成功后，运行下面两组代码做对比分析，但现在因为报错完全动不了：

1. Aging组间对比 #

contrast_Aging <- contrast(
  LME_01,
  a = list(Aging = c("1w"), Adhesive = levels(Data$Adhesive), Approach = levels(Data$Approach)),
  b = list(Aging = c("6m"), Adhesive = levels(Data$Adhesive), Approach = levels(Data$Approach))
)
c1 <- as.matrix(contrast$X)
Contrastsi2 <- summary(glht(LME_01, c1))

2. Approach组间对比 #

contrast_Approach <- contrast(
  LME_01,
  a = list(Approach = c("SE"), Aging = levels(Data$Aging), Adhesive = levels(Data$Adhesive)),
  b = list(Approach = c("ER"), Aging = levels(Data$Aging), Adhesive = levels(Data$Adhesive))
)
c2 <- as.matrix(contrast$X)
Contrastsi3 <- summary(glht(LME_01, c2))

真心希望各位能帮我解决这个奇异值的问题，让我能继续完成后续的分析！

内容的提问来源于stack exchange，提问作者Mohammed Ahmed