question about glm in R

[tujchl]

HI
I know I post my question about R here is somehow not appropriate, but I really hope someone can teach me.

I use glm in R to do logistic regression. and treat both response and predictor as factor
In my first try:

*******************************************************************************
Call:
glm(formula = as.factor(diagnostic) ~ as.factor(7161521) +
as.factor(2281517), family = binomial())

Deviance Residuals:
Min 1Q Median 3Q Max
-1.5370 -1.0431 -0.9416 1.3065 1.4331

Coefficients:
Estimate Std. Error z value Pr(>|z|)
(Intercept) -0.58363 0.27948 -2.088 0.0368 *
as.factor(7161521)2 1.39811 0.66618 2.099 0.0358 *
as.factor(7161521)3 0.28192 0.83255 0.339 0.7349
as.factor(2281517)2 -1.11284 0.63692 -1.747 0.0806 .
as.factor(2281517)3 -0.02286 0.80708 -0.028 0.9774
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

(Dispersion parameter for binomial family taken to be 1)

Null deviance: 678.55 on 498 degrees of freedom
Residual deviance: 671.20 on 494 degrees of freedom
AIC: 681.2

Number of Fisher Scoring iterations: 4
*******************************************************************************

And I remodel it and want no intercept:
*******************************************************************************
Call:
glm(formula = as.factor(diagnostic) ~ as.factor(2281517) +
as.factor(7161521) - 1, family = binomial())

Deviance Residuals:
Min 1Q Median 3Q Max
-1.5370 -1.0431 -0.9416 1.3065 1.4331

Coefficients:
Estimate Std. Error z value Pr(>|z|)
as.factor(2281517)1 -0.5836 0.2795 -2.088 0.0368 *
as.factor(2281517)2 -1.6965 0.6751 -2.513 0.0120 *
as.factor(2281517)3 -0.6065 0.8325 -0.728 0.4663
as.factor(7161521)2 1.3981 0.6662 2.099 0.0358 *
as.factor(7161521)3 0.2819 0.8325 0.339 0.7349
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

(Dispersion parameter for binomial family taken to be 1)

Null deviance: 691.76 on 499 degrees of freedom
Residual deviance: 671.20 on 494 degrees of freedom
AIC: 681.2

Number of Fisher Scoring iterations: 4
*******************************************************************************

As show above in my second model it return no intercept but look this:
Model1:
(Intercept) -0.58363 0.27948 -2.088 0.0368 *
Model2:
as.factor(2281517)1 -0.5836 0.2795 -2.088 0.0368 *

They are exactly the same. Could you please tell me what happen?

Thank you in advance

[cjp]

Maybe try here?:

http://stats.stackexchange.com/

[tujchl]

Thank you cjp, I`ll try it on your wesite

[Wolfgang Huber]

Tujchl,

the canonical place for such questions is the R-help mailing list on the R-Project's website.

Your formula expressions look complex to me, and I am not sure I understand your intention with (or the effect of) as.factor(2281517). Is '2281517' an integer constant or a variable name? On the risk of invoking a cliche, but perhaps some reading of the documentation of glm and of R's formula interface would be instructive.

Best wishes
Wolfgang