st: How can I compute a change in F-statistic using weighted data and "ologit"?

["Jennifer van Stelle" <jvanstel@hotmail.com>]

Hi -

I'm a relatively new Stata user, and have never posted to this list before.  
I've checked the FAQ, however, and don't see an answer to my problem, so I 
thought I'd post it here and hope for a response.

I'm using Stata 7.0 for UNIX, and am doing ordered logit models with survey 
data, using probability weights and primary sampling unit clustering (data 
is for individuals in 28 different countries).  Because I'm doing several 
different models (i.e., Model One with just the control variables, then 
Model Two with the controls plus a subset of independent variables, and 
finally Model Three with the controls and all the independent variables), 
I'd like to be able to tell whether each model is a significant improvement 
on the previous one.  I've been warned about what I should NOT to do (that 
is, don't simply subtract the F-statistic of Model One from Model Two, or 
Model Two from Model Three), but no one has been able to explain to me what 
I SHOULD do in order to calculate change in F in this particular situation.  
Can anyone tell me how to do this?

Any help will be gratefully accepted!

Thanks.

- Jen



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