On Aug 28, 2010, at 10:58 PM, Randklev, Charles wrote:
Hi,
I am trying to assemble a three-way contingency table examining the
presence/absence of mussels, water depth (Depth1 and Depth 2) and
water velocity (Flow vs. No Flow). I have written the following code
listed below; however, when run the glm I get the following message,
"Error in model.frame.default(formula = Count ~ MP + wd + wv,
drop.unused.levels = TRUE) : variable lengths differ (found for
'MP')". This may be something simple, if so I apologize. Any help
would be greatly appreciated.
Best,
C.R.
numbers <- c(1134,956,328,529,435,599,27,99)
dim(numbers) <- c(2,2,2)
numbers
dimnames(numbers)[[3]] <-list("Mussels", "No Mussels")
dimnames(numbers)[[2]] <- list("Flow", "No Flow")
dimnames(numbers)[[1]] <- list("Depth1", "Depth2")
ftable(numbers)
as.data.frame.table(numbers)
frame <- as.data.frame.table(numbers)
names(frame) <- c("wd", "wv", "MP", "Count")
frame
attach(frame)
model1 <- glm(Count~MP+wd+wv,poisson)
I don't get that error, so maybe you have more than one MP variable
after attaching "frame". Have you used ls() recently. If there is an
extra "MP" you should see it there but it shouldn't show up if it is
only attached. The attach function is a common cause of perplexing
errors.
--
David.
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