user3185925 - 3 months ago 16
R Question

# aov won't return pvalues in R

I have a strange problem with anova summary results

`summary(aov)`
.

So here is the problem. I have a dataset with 6 columns. Here is the dataset sample:

``````Panelist    Prod.ID Overall Appearance  Flavor  Texture
1   196 9   9   9   9
1   239 7   9   6   7
1   354 9   8   8   7
1   427 3   8   2   3
1   577 8   9   7   9
1   638 7   9   7   8
1   772 6   4   3   3
1   852 9   8   9   8
2   196 8   8   7   8
2   239 7   7   7   7
2   354 6   5   6   4
2   427 6   7   4   6
2   577 3   6   3   5
2   638 4   4   5   2
2   772 6   2   6   7
2   852 7   6   7   6
3   196 7   9   7   8
3   239 8   9   8   8
3   354 8   8   7   8
3   427 7   8   6   8
3   577 8   9   8   8
3   638 8   9   8   7
3   772 5   8   8   8
3   852 8   9   8   8
``````

Anyway the first two columns are the factors and the rest are the response variables. The Panelist and the Prod.ID are considered by the
`summary()`
as continuous variables, so I converted them to be a factors with
`as.factor()`
.

After that conversion I ran the anova-test with following model
`Overall ~ Panelist * Prod.ID`
, but as summary results I got only this:

``````> summary(aov(Overall ~ Prod.ID * Panelist, data = paneElements))

Df Sum Sq Mean Sq
Prod.ID             7  189.6  27.085
Panelist          160 1252.9   7.830
Prod.ID:Panelist 1116 3116.1   2.792
``````

I can't find any cause that makes the F-test values and P-values disappear.

Any help will be very appreciated.

Thanks a lot.

You have only one observation for each combination of `Prod.ID` and `Panelist` (at least in your sample data), so the number of groups is equal to the number of observations. This would cause a divide-by-zero in the F-Test, which may be the reason for the lack of reported F-Test and p-values.
For example, when I add an extra observation for `Prod.ID` 196 for just one level of `Panelist`, I get F and p values reported in the output.