[R-sig-ME] Mixed effects model with unbalanced repeated measures across blocks

[M West]

Hello,

I would like to double check that my model is 'OK'.
I am analyzing whether the density of nests differed across four different
forests. Design: I repeatedly sampled transects in the same four forests
throughout the breeding season (May - September). The question here is not
whether the density of nests differed each month (which is what most
examples I've found tend to ask), but I need to make sure to account for
the autocorrelation from repeatedly sampling each forest (i.e., each
transect at each forest).

This design is unbalanced: some sites were only sampled for 2 months,
others were sampled all 5 months and some sites have more transects
compared to others (to account for differences in the length of edges of
the forest). I don't know how to account for this unbalanced design.

The output is included.

Many thanks in advance
~M


model <- with(data, glmer(Number_of_Nests ~ Forest + Week +
(1|Forest:TransectID), family = poisson, data=data))
summary(model)
anova(model, Type = 'II')


Here is the output:


Generalized linear mixed model fit by maximum likelihood (Laplace
Approximation) ['glmerMod']
 Family: poisson  ( log )
Formula: Number_of_Nests ~ Forest+ Month + (1 | Forest:TransectID)
 Data: data

     AIC      BIC   logLik deviance df.resid
   555.1    577.1   -267.5    535.1       57

Scaled residuals:
    Min      1Q  Median      3Q     Max
-5.8501 -1.3650 -0.0699  0.9217  4.9935

Random effects:
 Groups          Name        Variance Std.Dev.
Forest:TransectID (Intercept) 0.5939   0.7707
Number of obs: 67, groups:  Forest:TransectID, 19

Fixed effects:
               Estimate Std. Error z value Pr(>|z|)
(Intercept)     1.64503    0.54558   3.015 0.002568 **
ForestA     1.03360    0.60045   1.721 0.085182 .
ForestB         -0.44092    0.72516  -0.608 0.543171
ForestC          1.90743    0.78368   2.434 0.014935 *
MonthMay       0.30640    0.08737   3.507 0.000453 ***
MonthJune      -1.11313    0.13132  -8.477  < 2e-16 ***
MonthJuly  -2.63123    0.25254 -10.419  < 2e-16 ***
MonthAugust   -1.34959    0.17249  -7.824 5.11e-15 ***
MonthSeptember -1.34612    0.72723  -1.851 0.064168 .
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

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