

   Dear list:

   I am using "multcomp" package to make post-hoc comparisons in a 7-level factor. The analysis performed is at follows:

> minclutchmodel2<-lmer(clsize2~mod+inslargest+briventralst+inslargest:briventralst+(1|site/pair)+(1|year),family=poisson) 
> cht<-glht(minclutchmodel2,linfct=mcp(mod="Tukey"))
> summary(cht, test = univariate())

         Simultaneous Tests for General Linear Hypotheses

Multiple Comparisons of Means: Tukey Contrasts


Fit: glmer(formula = clsize2 ~ mod + inslargest + briventralst + inslargest:briventralst + 
    (1 | site/pair) + (1 | year), family = poisson)

Linear Hypotheses:
               Estimate Std. Error z value Pr(>|z|)    
EC - E == 0  -0.5654710  0.5710626  -0.990 0.322072    
R - E == 0   -0.2080028  0.3590288  -0.579 0.562354    
RC - E == 0  -0.9835988  0.4836405  -2.034 0.041978 *  
S - E == 0   -1.3622236  0.3916350  -3.478 0.000505 ***
SC - E == 0  -0.0009705  0.4017037  -0.002 0.998072    
U - E == 0   -0.1578700  0.2907425  -0.543 0.587137    
R - EC == 0   0.3574681  0.5494919   0.651 0.515341    
RC - EC == 0 -0.4181278  0.6527767  -0.641 0.521823    
S - EC == 0  -0.7967526  0.5570890  -1.430 0.152658    
SC - EC == 0  0.5645005  0.6019210   0.938 0.348331    
U - EC == 0   0.4076009  0.5309090   0.768 0.442641    
RC - R == 0  -0.7755959  0.4543557  -1.707 0.087818 .  
S - R == 0   -1.1542208  0.3641393  -3.170 0.001526 ** 
SC - R == 0   0.2070323  0.3462441   0.598 0.549882    
U - R == 0    0.0501328  0.2431495   0.206 0.836650    
S - RC == 0  -0.3786249  0.4875128  -0.777 0.437368    
SC - RC == 0  0.9826283  0.4792105   2.051 0.040314 *  
U - RC == 0   0.8257287  0.4180611   1.975 0.048252 *  
SC - S == 0   1.3612531  0.4079427   3.337 0.000847 ***
U - S == 0    1.2043536  0.3058414   3.938 8.22e-05 ***
U - SC == 0  -0.1568995  0.2964628  -0.529 0.596640    
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
(Univariate p values reported)

 

   I was just wondering about the degrees of freedom of those z scores. As they're pairwise comparisons, I guess it's comparing the means of the 2 levels involved for each caso, so I would say the degrees of freedom for each should be 1. Am I right or is there something that I'm missing?
   Also, if I want to know the direction of the effect of the factor, I mean, which are the levels that are contributing more to the significant effect of the factor on the model, according to these data, would I say it's S>RC (both levels are significant, but S to a greater extent than RC)?

   Thank you very much.


    ________________________________________

   Iker Vaquero-Alba
   Centre for Ecology and Conservation
   Daphne du Maurier Building
   University of Exeter, Cornwall Campus
   Treliever Road
   TR10 9EZ Penryn
   U.K.

   http://biosciences.exeter.ac.uk/cec/staff/postgradresearch/ikervaquero-alba/
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