[R] Can't find all levels of categorical predictors in output of zeroinfl()

[j.straka]

Hello,
I’m using zero-inflated Poisson regression via the zeroinfl() function to
analyze data on seed-set of plants, but for some reason, I don’t seem to be
getting the output for all three levels of my two categorical predictors. 

More about my data and model:
My response variable is the number of viable seeds (AVInt), and my two
categorical predictors are elevation (Elev) and Treatment (Treatment).  Elev
has three levels: 01-Low, 02-Mid, and 03-High; Treatment also has three
possibilities: B, F, or O. 

Because the response variable (AVInt) is zero-inflated and
Poisson-distributed, I’m using zeroinfl() under the pcsl library as an
alternative to factorial ANOVA (I’ve also tried the zero-inflated negative
binomial).  This is early in my data-analysis, but I will likely incorporate
additional categorical and continuous predictors at a later time. 

This gives me the following model:

zipclay=zeroinfl(AVInt ~ Elev + Treatment)

So running the model, I have: 
> zipclay=zeroinfl(AVInt ~ Elev + Treatment)
> summary(zipclay)

Call:
zeroinfl(formula = AVInt ~ Elev + Treatment)

Pearson residuals:
    Min      1Q  Median      3Q     Max 
-1.1958 -0.5612 -0.3764  0.2704  5.5130 

Count model coefficients (poisson with log link):
            Estimate Std. Error z value Pr(>|z|)   
(Intercept)  -0.2035     0.3435  -0.592  0.55368   
Elev02-Mid    0.3937     0.1806   2.180  0.02923 * 
Elev03-High   0.1635     0.1792   0.912  0.36159   
TreatmentF    1.0026     0.3305   3.033  0.00242 **
TreatmentO    0.5915     0.3293   1.796  0.07244 . 

Zero-inflation model coefficients (binomial with logit link):
            Estimate Std. Error z value Pr(>|z|)    
(Intercept)   1.6086     0.5080   3.167  0.00154 ** 
Elev02-Mid   -0.3813     0.4345  -0.878  0.38020    
Elev03-High  -0.9512     0.4532  -2.099  0.03584 *  
TreatmentF   -0.9774     0.4690  -2.084  0.03718 *  
TreatmentO   -3.0242     0.6561  -4.609 4.05e-06 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 

Number of iterations in BFGS optimization: 16 
Log-likelihood: -363.2 on 10 Df

So my question is, where did my "Elev01-Low" and "TreatmentB" go??  Why
aren't they appearing in the output table? 

Any insight would be greatly appreciated!

- Jason



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