[R] nontabular logistic regression

From: Jeffrey Stratford <stratja_at_auburn.edu>
Date: Fri 13 Oct 2006 - 14:28:23 GMT


Hi. I'm attempting to fit a logistic/binomial model so I can determine the influence of landscape on the probability that a box gets used by a bird. I've looked at a few sources (MASS text, Dalgaard, Fox and google) and the examples are almost always based on tabular predictor variables. My data, however are not. I'm not sure if that is the source of the problems or not because the one example that includes a continuous predictor looks to be coded exactly the same way. Looking at the output, I get estimates for each case when I should get a single estimate for purbank. Any suggestions?

Many thanks,

Jeff

THE DATA: (200 boxes total, used [0 if unoccupied, 1 occupied], the rest are landscape variables).

box	use	purbank	purban2	purban1	pgrassk	pgrass2	pgrass1	grassdist	grasspatchk
1	1	0.003813435	0.02684564	0.06896552	0.3282487	0.6845638	0.7586207	0	3.73
2	1	0.04429451	0.1610738	0.1724138	0.1534174	0.3825503	0.6551724	0	1.023261
3	1	0.04458785	0.06040268	0	0.1628043	0.557047	0.7586207	0	0.9605769
4	1	0.06072162	0.2080537	0.06896552	0.01936052	0	0	323.1099	0.2284615
5	0	0.6080962	0.6979866	0.6896552	0.03168084	0.1275168	0.2413793	30	0.2627027
6	1	0.6060428	0.6107383	0.3448276	0.04077442	0.2885906	0.4482759	30	0.2978571
7	1	0.3807568	0.4362416	0.6896552	0.06864183	0.03355705	0	94.86833	0.468
8	0	0.3649164	0.3154362	0.4137931	0.06277501	0.1275168	0	120	0.4585714

THE CODE: box.use<- read.csv("c:\\eabl\\2004\\use_logistic2.csv", header=TRUE) attach(box.use)
box.use <- na.omit(box.use)
use <- factor(use, levels=0:1)
levels(use) <- c("unused", "used")
glm1 <- glm(use ~ purbank, binomial)

THE OUTPUT: Coefficients:

                     Estimate Std. Error   z value Pr(>|z|)
(Intercept)        -4.544e-16  1.414e+00 -3.21e-16    1.000
purbank0            2.157e+01  2.923e+04     0.001    0.999
purbank0.001173365  2.157e+01  2.067e+04     0.001    0.999
purbank0.001466706  2.157e+01  2.923e+04     0.001    0.999
purbank0.001760047  6.429e-16  2.000e+00  3.21e-16    1.000
purbank0.002346729  2.157e+01  2.923e+04     0.001    0.999
purbank0.003813435  2.157e+01  2.923e+04     0.001    0.999
purbank0.004106776  2.157e+01  2.067e+04     0.001    0.999
purbank0.004693458  2.157e+01  2.067e+04     0.001    0.999


****************************************
Jeffrey A. Stratford, Ph.D.
Postdoctoral Associate
331 Funchess Hall
Department of Biological Sciences
Auburn University
Auburn, AL 36849
334-329-9198
FAX 334-844-9234
http://www.auburn.edu/~stratja

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