 

Hi All,

I am new to the use of R and to GLMM's. I am not sure how to interpret my
results. I first modeled my most complex model with all of my hypothesized
fixed effects(print out below). From my Pr(>|z|) values I feel that I should
be able to say that none of the fixed effects significantly affects
presence. I also ran models in which I took out one fixed effect at a time
and compare using ANOVA. I also started with more basic models (1 fixed
effect) and compared it to a model with only random effects (with the #1 in
place of where the fixed effect would be). Using ANOVA I also compared those
models. What is confusing to me is that I sometimes get lower AIC values and
significant p-values for the ANOVA with the model with a single fixed effect
vs. a model with no fixed effect. I was expecting based on the Pr(>|z|)
values that I would get lower AIC values for the no fixed effects model. For
any variation that I run on the model (1-7 fixed effects), the Pr(>|z|)
values are always >0.05. Can someone help explain this to me? I'm really
sorry if this something that has already been addressed, but I couldn't find
anything on the message boards similar to my question. 

Thanks!

 

 

print(m1<-lmer(Presence ~FixedEffect1 + FixedEffect2 + FixedEffect3 +
FixedEffect4 + FixedEffect5 + FixedEffect6 + FixedEffect7 + (1|Site) +
(1|Year), family=binomial, REML=FALSE))

Generalized linear mixed model fit by the Laplace approximation 

Formula: Presence ~FixedEffect1 + FixedEffect2 + FixedEffect3 + FixedEffect4
+ FixedEffect5 + FixedEffect6 + FixedEffect7  + (1 | Site) + (1 | Year) 

  AIC   BIC logLik deviance

 88.9 110.8 -34.45     68.9

Random effects:

 Groups Name        Variance Std.Dev.

 Site   (Intercept)  0        0      

 Year   (Intercept)  0        0      

Number of obs: 66, groups: Site, 4; Year, 2

 

Fixed effects:

                  Estimate Std. Error z value Pr(>|z|)  

(Intercept)     -17.793834   9.299257  -1.914   0.0557 .

FixedEffect1        0.164940   0.175818   0.938   0.3482  

FixedEffect2         0.068806   0.057713   1.192   0.2332  

FixedEffect3      -0.004817   0.004070  -1.183   0.2367  

FixedEffect4          0.375625   0.399966   0.939   0.3477  

FixedEffect5          -0.112683   0.658858  -0.171   0.8642  

FixedEffect6  2.672537   2.158679   1.238   0.2157  

FixedEffect7       -0.175103   0.132223  -1.324   0.1854  

---

Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 

 

Correlation of Fixed Effects:

            (Intr) Fix1 Fix2 Fix3 Fix4 Fix5 Fix6 Fix7

FixedEffect1  -0.050                                          

FixedEffect2   -0.801 -0.226                                   

FixedEffect3   0.731 -0.098 -0.848                            

FixedEffect4  -0.577 -0.055  0.144 -0.036                     

FixedEffect5      0.130  0.284  0.009 -0.335 -0.695              

FixedEffect6 -0.035  0.282 -0.086  0.062 -0.010 -0.193       

FixedEffect7   0.120 -0.386  0.037 -0.068 -0.265  0.223 -0.338


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