
Dear R users,
I would like some advice on how to procede with a glmmPQL that I am developing, specifically the interaction factor. The model is run on count data and the interaction I am interested in is between "distcat" a two level categorical factor (0,1) and "isolateds" a three level categorical factor (0,1,2). The output from the model indicates there is a significant interaction and a plot of the data confirms this. However what I am wondering is if there is a way for the model to test and provide output for the overall interaction term distcat:isolateds, rather than the output distcat1:isolateds1, distcat1:isolateds2 produced in the model below?
Any suggestions on how I can get the overall interaction significance would be greatly appreciated.
Many thanks
Claire
 

 
> allterms<-glmmPQL(sumvisab~distcat+isolateds+distcat:isolateds+open,random=~1|site/distance/obsday,family=poisson)

> summary(allterms)
Linear mixed-effects model fit by maximum likelihood
 Data: NULL 
  AIC BIC logLik
   NA  NA     NA
Random effects:
 Formula: ~1 | site
        (Intercept)
StdDev:   0.3659353
 Formula: ~1 | distance %in% site
         (Intercept)
StdDev: 5.712825e-05
 Formula: ~1 | obsday %in% distance %in% site
        (Intercept) Residual
StdDev:   0.5649947 1.017531
Variance function:
 Structure: fixed weights
 Formula: ~invwt 
Fixed effects: sumvisab ~ distcat + isolateds + distcat:isolateds + open 
                         Value  Std.Error  DF   t-value p-value
(Intercept)          0.8687787 0.20928812 527  4.151114  0.0000
distcat1            -0.6031979 0.18187793  19 -3.316498  0.0036
isolateds1          -0.5934423 0.25153278  19 -2.359304  0.0292
isolateds2          -0.0021440 0.29075913  19 -0.007374  0.9942
open                 0.0091916 0.00139872 527  6.571468  0.0000
distcat1:isolateds1  0.5690202 0.25334775  19  2.246004  0.0368
distcat1:isolateds2  0.0713179 0.29205476  19  0.244193  0.8097
 Correlation: 
                    (Intr) dstct1 isltd1 isltd2 open   dst1:1
distcat1            -0.417                                   
isolateds1          -0.645  0.340                            
isolateds2          -0.544  0.294  0.445                     
open                -0.509  0.019  0.056  0.020              
distcat1:isolateds1  0.312 -0.718 -0.489 -0.211 -0.039       
distcat1:isolateds2  0.260 -0.623 -0.212 -0.477 -0.012  0.447
Standardized Within-Group Residuals:
       Min         Q1        Med         Q3        Max 
-2.1426196 -0.7806017 -0.1000826  0.5241608  3.6147033 
Number of Observations: 660
Number of Groups: 
                          site             distance %in% site obsday %in% distance %in% site 
                            22                             44                            132  


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