ESTIMATES SURVIVAL ANALYSIS WEIBULL

Dear members,



I did a survival analysis, Weibul fits better for my data: this is the "head" of my data



 start stop state soil volatile hours replicate
1     0   48     1   ca       nc    48         3
2     0   48     1   ca       nc    48         4
3     0   48     1   ca       nc    48         5
4     0   48     1   ca       nc    48         8
5     0   60     1   ca        c    60         1
6     0   60     1   ca        c    60         1





I have 4 soils: ca, cs, cl and sand



and I have 2 volatiles: nc and c



However, when I get the stimates my soil "ca" does not appear and the volatile "c" neither



Call:
survreg(formula = Surv(hours, state) ~ soil * volatile, data = surgal,
    dist = "weibull")
                      Value Std. Error      z         p
(Intercept)          4.3605     0.0417 104.51  0.00e+00
soilcl              -0.0784     0.0590  -1.33  1.84e-01
soilcs              -0.3865     0.0567  -6.81  9.59e-12
soilsand            -0.1913     0.0579  -3.30  9.61e-04
volatilenc          -0.1600     0.0579  -2.76  5.74e-03
soilcl:volatilenc    0.1320     0.0823   1.60  1.09e-01
soilcs:volatilenc    0.2679     0.0812   3.30  9.64e-04
soilsand:volatilenc  0.0821     0.0809   1.01  3.10e-01
Log(scale)          -1.4788     0.0442 -33.46 1.73e-245

Scale= 0.228

Weibull distribution
Loglik(model)= -1036.3   Loglik(intercept only)= -1065
        Chisq= 57.41 on 7 degrees of freedom, p= 5e-10
Number of Newton-Raphson Iterations: 5
n= 257



Anyone knows why? or what does it mean? how should I interpret the values in the table?



Thanks for your help,



Xavier