[R] A warning message in glht

[ONKELINX, Thierry]

Dear Yulia,

When you have an interaction between a continuous and a categorical variable, then the multiple comparison on the categorical variabel makes only sense conditional that the continuous variable is zero. Hence the warning.

Best regards,

Thierry

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx at inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey


-----Oorspronkelijk bericht-----
Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Namens Yuliia Aloshycheva
Verzonden: woensdag 7 november 2012 21:52
Aan: r-help at r-project.org
Onderwerp: [R] A warning message in glht

Dear all,

I was wondering if you could give me any suggestions/help on the following issue. So I carried out the analysis of my data using generalized linear model (glm). After that, to check for multiple comparisons, I applied the glht function from the multcomp package in R. The output, however, gave me a warning (please see below). So my question is whether this warning is smth that I should ignore or not. And if not, what I should do about it (I kind of know how to deal with this problem for categorical factors, however, in my data, one of the factors (AveScore) is continuous).

Thanks a lot!

           Yuliia

   Simultaneous Tests for General Linear Hypotheses

Multiple Comparisons of Means: Tukey Contrasts

Fit: glm(formula = EW1 ~ AveScore + Speaker + File + factor(Bplace) +
    factor(Sex) + AveScore:File, family = binomial(link = "logit"),
    data = data.0)

Linear Hypotheses:
            Estimate Std. Error z value Pr(>|z|)
In - A == 0  -0.9055     0.3573  -2.534   0.0302 *
O - A == 0   -2.5638     0.3917  -6.545   <0.001 ***
O - In == 0  -1.6584     0.3766  -4.404   <0.001 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 (Adjusted p values reported -- single-step method)

*Warning message: In mcp2matrix(model, linfct = linfct) :  covariate interactions found -- default contrast might be inappropriate*





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