Hi all, I am trying to run a glm with mixed effects. My response variable is number of seedlings emerging; my fixed effects are the tree species and distance from the tree (in two classes - near and far).; my random effect is the individual tree itself (here called Plot). The command I've used is:
mod <- glmer(number ~ Species + distance + offset(area) + (1|Plot), family = poisson) There is an area offset because the plot in which seedlings were counted was a wedge with its point at the tree base, and therefore the area of the part of plot far from the tree was greater than the area of the plot closer to the tree. The results I'm getting are: Generalized linear mixed model fit by the Laplace approximation Formula: number ~ Species + distance + offset(area) + (1 | Plot) AIC BIC logLik deviance 145.6 168.7 -64.82 129.6 Random effects: Groups Name Variance Std.Dev. Plot (Intercept) 0.60205 0.77592 Number of obs: 132, groups: Plot, 132 Fixed effects: Estimate Std. Error z value Pr(>|z|) (Intercept) -138.8423 0.4704 -295.1 < 2e-16 *** SpeciesCr -0.9977 0.6259 -1.6 0.11091 SpeciesDb -1.2140 0.6945 -1.7 0.08046 . SpeciesHk -2.0864 1.2134 -1.7 0.08553 . SpeciesPa -2.6245 1.2063 -2.2 0.02958 * SpeciesPs 1.3056 0.4027 3.2 0.00119 ** distancen 121.7170 0.3609 337.3 < 2e-16 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 Correlation of Fixed Effects: (Intr) SpcsCr SpcsDb SpcsHk SpecsP SpcsPs SpeciesCr -0.423 SpeciesDb -0.391 0.295 SpeciesHk -0.223 0.169 0.152 SpeciesPa -0.222 0.170 0.153 0.088 SpeciesPs -0.732 0.507 0.458 0.262 0.263 distancen -0.648 -0.020 -0.002 -0.003 -0.006 0.085 Here, clearly, distance from the tree has an effect, but I want to know whether the identity of the species influences seedling numbers in general. I am unable, however, to make much sense of the output. Also, what does correlation of fixed effects really tell me? Many thanks for any help. Cheers, Umesh Srinivasan, Bangalore, India ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.