[R] Fixed zeros in tables

[Andrew Robinson]

Hi Andrew,

try the weights argument - apply zero weight to the structural zeros,
and 1 elsewhere.

Cheers

Andrew

On Sun, Nov 26, 2006 at 11:39:39AM +0700, A.R. Criswell wrote:
> Hello All R Users,
> 
> Function loglm() in library MASS can be cajoled to accomodate
> structural zeros in a cross-classification table. An example from
> Fienberg demonstrates how this can be done.
> 
> My question is: Can the function glm() perform the same task? Can
> glm() estimate a log-linear model with fixed zeros like loglm()?
> 
> Thanks for your help,
> Andrew
> 
> ## Fienberg, The Analysis of Cross-Classified Contingency Tables, 2nd
> ed., p.148.
> ## Results from survey of teenagers regarding their health concerns.
> 
> health <- data.frame(expand.grid(CONCERNS = c("sex", "menstral",
>                                               "healthy", "nothing"),
>                                  AGE      = c("12-15", "16-17"),
>                                  GENDER   = c("male", "female")),
>                                  COUNT    = c(4, 0, 42, 57, 2, 0, 7, 20,
>                                               9, 4, 19, 71, 7, 8, 10, 21))
> 
> health <- xtabs(COUNT ~ CONCERNS + AGE + GENDER, data = health)
> 
> zeros <- data.frame(expand.grid(CONCERNS = c("sex", "menstral",
>                                               "healthy", "nothing"),
>                                 AGE      = c("12-15", "16-17"),
>                                 GENDER   = c("male", "female")),
>                                 COUNT    = c(1, 0, 1, 1, 1, 0, 1, 1,
>                                              1, 1, 1, 1, 1, 1, 1, 1))
> 
> zeros <- xtabs(COUNT ~ CONCERNS + AGE + GENDER, data = zeros)
> 
> library(MASS)
> 
> fm.1 <- loglm(~ CONCERNS + AGE + GENDER,
>               data = health, start = zeros, fitted = TRUE)
> 
> fm.1; round(fm.1$fitted, 1)
> 
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-- 
Andrew Robinson  
Department of Mathematics and Statistics            Tel: +61-3-8344-9763
University of Melbourne, VIC 3010 Australia         Fax: +61-3-8344-4599
http://www.ms.unimelb.edu.au/~andrewpr
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