Use alias() to help here.
It is likely that one of S T L only occurs (or does not occur) at level 6
of C.
On Wed, 19 Apr 2006, voodooochild at gmx.de wrote:
> Hello,
>
> i have the following model,
>
> poi1<-glm(F~S+T+L+C,family=poisson,x=T)
>
> where F,S,T,L are metric and C is a factor variable with the levels
"0",
> "1", "2", "3", "4", "5"
and "6"
>
> if i do summary(poi1), i get the following
>
> Call:
> glm(formula = F ~ S + T + L + C, family = poisson, x = T)
>
> Deviance Residuals:
>
> Min 1Q Median 3Q Max
>
> -2.44054 -0.80997 -0.04627 0.69402 2.90301
>
> Coefficients: (1 not defined because of singularities)
> Estimate Std. Error z value Pr(>|z|)
>
> (Intercept) -10.45553 1.16221 -8.996 < 2e-16 ***
>
> S 1.08024 0.13609 7.938 2.06e-15 ***
>
> T 1.63582 0.05170 31.643 < 2e-16 ***
>
> L 3.31684 0.49965 6.638 3.17e-11 ***
>
> C1 0.21256 0.16449 1.292 0.1963
>
> C2 -0.10895 0.06675 -1.632 0.1027
>
> C3 0.15159 0.06992 2.168 0.0302 *
>
> C4 0.50949 0.05870 8.680 < 2e-16 ***
>
> C5 0.11240 0.01686 6.667 2.61e-11 ***
>
> C6 NA NA NA NA
>
> ---
>
> Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05
'.' 0.1 ' ' 1
>
> (Dispersion parameter for poisson family taken to be 1)
>
> Null deviance: 47365.29 on 495 degrees of freedom
>
> Residual deviance: 574.64 on 487 degrees of freedom
>
> AIC: 4091.8
>
> Number of Fisher Scoring iterations: 4
>
>
> my question now is why do i get those "singularities" and where
do they
> come from, i guess because of the singularites i get the NA's, what can
> i do here to avoid them?
> I think i have done some wrong dummy coding or something like that? By
> the way, i have 7 levels and only got estimates for 6 levels, whats
> wrong here?
>
> best regards
> andreas
>
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--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595