R:在 anova.lm(g) 中:对基本完美拟合的 ANOVA F 检验是不可靠的 [英] R: In anova.lm(g) : ANOVA F-tests on an essentially perfect fit are unreliable

问题描述

我正在将在线指南与旧文本配对以学习 R(第 182 页 - http://cran.r-project.org/doc/contrib/Faraway-PRA.pdf).当我使用 R 包中的数据时(如教程示例中所示)，没有问题.但是，当我使用文本中的数据时，我总是以没有 F 值和警告结束.

I am pairing up online guides with an old text to learn R (page 182 - http://cran.r-project.org/doc/contrib/Faraway-PRA.pdf). When I use data from a package from R (as in the tutorial examples) there is no problem. However, when I use data from my text, I always end with no F-value and the warning.

看看:

将数据转换为 data.frame:

data into a data.frame:

car.noise <- data.frame( speed = c("idle", "0-60mph", "over 60"), chrysler = c(41,65,76), 
bmw = c(45,67,72), ford = c(44,66,76), chevy = c(45,66,77), subaru = c(46,76,64))

检查数据框:

car.noise
    speed chrysler bmw ford chevy subaru
1    idle       41  45   44    45     46
2 0-60mph       65  67   66    66     76
3 over 60       76  72   76    77     64

熔化数据框:

mcar.noise<- melt(car.noise, id.var="speed")

检查融化的data.frame

check melted data.frame

> mcar.noise
     speed variable value
1     idle chrysler    41
2  0-60mph chrysler    65
3  over 60 chrysler    76
4     idle      bmw    45
5  0-60mph      bmw    67
6  over 60      bmw    72
7     idle     ford    44
8  0-60mph     ford    66
9  over 60     ford    76
10    idle    chevy    45
11 0-60mph    chevy    66
12 over 60    chevy    77
13    idle   subaru    46
14 0-60mph   subaru    76
15 over 60   subaru    64

执行方差分析并得到警告:

perform anova and get warning:

> anova(lm(value ~ variable * speed, mcar.noise))
Analysis of Variance Table

Response: value 
               Df  Sum Sq Mean Sq F value Pr(>F)
variable        4    6.93    1.73               
speed           2 2368.13 1184.07               
variable:speed  8  205.87   25.73               
Residuals       0    0.00                       
Warning message:
In anova.lm(lm(value ~ variable * speed, mcar.noise)) :
  ANOVA F-tests on an essentially perfect fit are unreliable

我能想到的唯一两种解释:

The only 2 explanations I can come up with:

1:我编码不正确2:文本示例太完美"了，因为它们试图显示清晰的示例

1: I am coding incorrectly 2: Text examples are too 'perfect' of a fit since they are trying to show clear example

推荐答案

您正在尝试拟合一个模型，该模型为每个可变*速度组合提供单独的均值.有了您拥有的数据，这意味着您根本没有任何复制.当每个组中只有一个值时，这就像尝试比较两个组一样.

You are trying to fit a model that gives a separate mean to every combination of variable*speed. With the data you have that means you don't have any replication at all. It would be like trying to compare two groups when you only have a single value from each group.

如果您查看方差分析表中的残差"行，您应该注意到那里没有任何自由度，并且平方和也为 0.如果您认为合适，但您没有足够的数据来拟合具有交互作用的模型，您可以尝试在没有交互的情况下拟合模型.

If you look at the line for "Residuals" in your anova table you should notice that you don't have any degrees of freedom there and your sums of squares are 0 as well. You could try to fit a model without an interaction if you feel it is appropriate but you don't have enough data to fit a model with an interaction.

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