[R] glm with binomial errors - problem with overdispersion

[peter dalgaard]

On Jun 14, 2011, at 09:53 , Anna Mill wrote:

> 
> Also note that success+failure is exactly 102 in fragment 1 and 105 in fragment 2, as is the sum of the successes for each fragment (of course it has to to make exactly 1/4). It is rather easy to suspect that it is actually a 0/1 coding of the type (as in "tick exactly one box"), and not independent binomial data.
>  
> sorry for the dumb question: so do you think, that my data is independent and the model appropriate?  
> Thanks, Anna
> 

Well, it's your data, and only you can tell what the original data looks like. We can only _suspect_ that they might be generated to be mutually exclusive. 

If you do not have independent binomial data, then a glm(..., binomial) will be seriously inappropriate (and a simple chi-square on the table of "successes" by type and fragment will be the obvious thing to do).


> 
> 
> --
> Peter Dalgaard
> Center for Statistics, Copenhagen Business School
> Solbjerg Plads 3, 2000 Frederiksberg, Denmark
> Phone: (+45)38153501
> Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com
> 
> 

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com