Greetings.
I'm a Master's student working on an analysis of herbivore damage on plants.
I have a tried running a glm with one categorical predictor (aphid
abundance) and a binomial response (presence/absence of herbivore damage).
My predictor has four categories: high, medium, low, and none. I used the
"ordered" function to sort my categories for a glm.
ah <-
read.csv("http://depot.northwestern.edu/class/2012WI_PBC_435-0_AND_BIOL_SCI_313/muller/herbivoryEdit.csv";)
ah1<- ah[ah$date=="110810",]
ah2<-ah[ah$date=="110904",]
aphidOrder <- ordered(ah2$aphidLevelMax,levels=c("none", "low", "med",
"high"))
ordAph <- glm(chewholebinom~aphidOrder,family=binomial,data=ah2)
When I ran the summary for the glm (output pasted below), I could not tell
which intercept referred to which factor level. My question is, what do .L,
.Q, and .C mean and how can I relate these factors to my original factors
(none, low, med, high)?
Thank you for your help,
Katherine
summary(ordAph)
Call:
glm(formula = chewholebinom ~ aphidOrder, family = binomial,
data = ah2)
Deviance Residuals:
Min 1Q Median 3Q Max
-1.6512 -0.9817 0.7687 0.7687 1.5353
Coefficients:
Estimate Std. Error z value Pr(>|z|)
(Intercept) -0.05567 0.25097 -0.222 0.8245
aphidOrder.L -1.36755 0.49366 -2.770 0.0056 **
aphidOrder.Q 0.36824 0.50195 0.734 0.4632
aphidOrder.C -0.09840 0.51011 -0.193 0.8470
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
(Dispersion parameter for binomial family taken to be 1)
Null deviance: 137.99 on 99 degrees of freedom
Residual deviance: 124.05 on 96 degrees of freedom
AIC: 132.05
Number of Fisher Scoring iterations: 4
--
View this message in context:
http://r.789695.n4.nabble.com/interpreting-the-output-of-a-glm-with-an-ordered-categorical-predictor-tp4440383p4440383.html
Sent from the R help mailing list archive at Nabble.com.
______________________________________________
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.
