[R] paradox about the degree of freedom in a logistic regression model

[Bin Yue]

 Dear all:
   "predict.glm" provides an example to perform logistic regression when the
response variable is a tow-columned  matrix. I find some paradox about the
degree of freedom  .
 > summary(budworm.lg)

Call:
glm(formula = SF ~ sex * ldose, family = binomial)

Deviance Residuals: 
     Min        1Q    Median        3Q       Max  
-1.39849  -0.32094  -0.07592   0.38220   1.10375  

Coefficients:
            Estimate Std. Error z value Pr(>|z|)    
(Intercept)  -2.9935     0.5527  -5.416 6.09e-08 ***
sexM          0.1750     0.7783   0.225    0.822    
ldose         0.9060     0.1671   5.422 5.89e-08 ***
sexM:ldose    0.3529     0.2700   1.307    0.191    
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

(Dispersion parameter for binomial family taken to be 1)

    Null deviance: 124.8756  on 11  degrees of freedom
Residual deviance:   4.9937  on  8  degrees of freedom
AIC: 43.104

Number of Fisher Scoring iterations: 4

This is the data set used in regression:
  numdead numalive sex ldose
1        1       19   M     0
2        4       16   M     1
3        9       11   M     2
4       13        7   M     3
5       18        2   M     4
6       20        0   M     5
7        0       20   F     0
8        2       18   F     1
9        6       14   F     2
10      10       10   F     3
11      12        8   F     4
12      16        4   F     5

     The degree of freedom is 8. Each row in the example is thought to be
one observation. If  I extend it to be a three column data.frame, the first
denoting the whether the individual is alive , the secode denoting the sex,
and the third "ldose",there will be 12*20=240 observations. 
     Since my data set is one of the second type , I wish to know whether
the form of data set affects the result of regression ,such as the degree of
freedom.
   Dose anybody have any idea about this? Thank all who read this message.
   Regards,
   Bin Yue

-----
Best regards,
Bin Yue

*************
student for a Master program in South Botanical Garden , CAS

-- 
View this message in context: http://www.nabble.com/paradox-about-the-degree-of-freedom-in-a-logistic-regression-model-tf4960753.html#a14208306
Sent from the R help mailing list archive at Nabble.com.