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Re: st: RE: how to choose between geographical identifiers??

From   "Ada Ma" <>
Subject   Re: st: RE: how to choose between geographical identifiers??
Date   Thu, 9 Mar 2006 12:55:03 +0000

Hi Nick,

Thanks for the reply - was hoping to reply to you straight away but
Googole mail was down so I could read your reply on RSS feed but could
not reply it!

Yes - you're right, I'm estimating the equation with hundreds of
dummies.  And I agree with you that the finer mesh will produce better
results.  I'm looking to see what kind of geographical boundaries will
better describe the variation in wage differentials and I'm not quite
sure how to proceed, thus the question.

Thanks for your help.


On 3/8/06, Nick Cox <> wrote:
> I am a geographer but I don't know much about (what is
> usually called human) geography. I regarded it as my main field
> of interest between 1968 and 1969, but no longer. There aren't
> many geographers on this list, I think.
> However, your question is not really geographical. I guess
> from this that you are using lots of dummies in each case
> and for once the answer is whichever set of dummies gives
> you a better model, according to your criteria of model
> excellence (my favourite criterion is usually minimal
> structure in residuals).
> In broad terms both LADs and TTWAs are fairly heterogeneous
> as both spring from a idea of an area functioning together
> rather than formal similarity of anything. So knowing the
> area might not help enormously in predicting wage. But
> whichever spatial subdivision has a finer mesh should
> prove better.
> Nick
> Ada Ma
> > I have a bunch of wage observations and all the observations are
> > attached with two geographical identifiers - local authority districts
> > (LADs) and travel to work areas (TTWAs).  I want to find out how wages
> > vary across different areas in UK.
> >
> > Now I can run wage estimations using either one of the two categorical
> > variables as explanatory variable.  I would however like to find out
> > which categorical variable fits the data better.  How do I compare the
> > two sets of results given that the explanatory variables are quite
> > different?
> >
> > Could you recommend what kind of tests I should use and if you are a
> > geographer, could you tell me are there any criteria that are used by
> > geographers to choose between different definitions of geographies
> > (regions, as opposed to LADs, as opposed to TTWAs, etc.)
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Ada Ma
Research Fellow
Health Economics Research Unit
University of Aberdeen, UK.
Tel: +44 (0) 1224 553863
Fax: +44 (0) 1224 550926

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