Hello,
I am running into trouble with an ANCOVA model I am attempting to
develop. The model includes 2 categorical variables (BHCODE and
MHCODE), 2 continuous variables (LOGWGT,LOG1980), and an interaction
term (BHCODE:MHCODE). There are seven levels of the BHCODE (ForestG,
ForestO, Generalist, Grassland, Scrub, Urban, Wetland) and three
levels of MHCODE (Neo, Res, Short). The model is written as follows:
lm7 <- lm(LOGIT1980~BHCODE+MHCODE+LOGWGT+LOG1980+BHCODE:MHCODE,data = data80)
When I attempt to use the summary(lm) function, I receive the
following output. Two terms are missing from all of my analyses,
ForestG (from the BHCODE variable) and Neo (from the MHCODE variable).
They are not constant and change throughout the data set. In
addition, the singularity warning does not seem to relate to these
missing levels but to the NA findings below
(BHCODEGeneralist:MHCODERes and BHCODEScrub:MHCODERes). I know that
ForestG is represented by the (Intercept) term, but it is not found
again in any interaction terms and Neo is just plain gone. Any
thoughts?? Thanks!
Coefficients: (2 not defined because of singularities)
Estimate Std. Error t value Pr(>|t|)
(Intercept) -0.19623 0.14485 -1.355 0.1795
BHCODEForestO -0.44754 0.18855 -2.374 0.0201 *
BHCODEGeneralist -0.06299 0.17215 -0.366 0.7154
BHCODEGrassland -0.47554 0.25435 -1.870 0.0653 .
BHCODEScrub -0.05577 0.21577 -0.258 0.7967
BHCODEUrban -0.35241 0.18748 -1.880 0.0639 .
BHCODEWetland -0.04488 0.14080 -0.319 0.7508
MHCODERes 0.37879 0.17125 2.212 0.0299 *
MHCODEShort -0.23582 0.16185 -1.457 0.1492
LOGWGT 0.19212 0.09511 2.020 0.0469 *
LOG1980 0.77477 0.06480 11.957 <2e-16 ***
BHCODEForestO:MHCODERes 0.26818 0.44155 0.607 0.5454
BHCODEGeneralist:MHCODERes NA NA NA NA
BHCODEGrassland:MHCODERes -0.99372 0.47383 -2.097 0.0393 *
BHCODEScrub:MHCODERes NA NA NA NA
BHCODEUrban:MHCODERes -0.73341 0.31685 -2.315 0.0233 *
BHCODEWetland:MHCODERes -0.79203 0.40175 -1.971 0.0523 .
BHCODEForestO:MHCODEShort 0.53082 0.30627 1.733 0.0871 .
BHCODEGeneralist:MHCODEShort 0.48821 0.27064 1.804 0.0752 .
BHCODEGrassland:MHCODEShort 0.38084 0.31552 1.207 0.2311
BHCODEScrub:MHCODEShort 0.25202 0.31288 0.805 0.4230
BHCODEUrban:MHCODEShort 0.44703 0.27947 1.600 0.1138
BHCODEWetland:MHCODEShort 0.24110 0.23742 1.016 0.3130
--
Benjamin Zuckerberg
Doctoral Candidate
State University of New York
College of Environmental Science and Forestry
Illick 244A, 1 Forestry Drive
Syracuse, New York 13210
Tele: (315) 470-6985
E-mail: bzuckerb at syr.edu