Re: st: Generating indices over nominal data?

[Andrea Bennett <mac.stata@gmail.com>]

Thank you very much for the helpful comment!

I will have a look at all your suggestions…

Best, Andrea

On Jun 21, 2012, at 12:42 , Maarten Buis wrote:

> On Thu, Jun 21, 2012 at 12:21 PM, Andrea Bennett wrote:
>> I have data on individual background knowledge
>> on 10 different topics. 3 of the topics are theoretically
>> similar (e.g. knowledge on public goods or
>> common pool resources or market externalities
>> could be considered as linked). For each item I have
>> a 3-point scale that says "no knowledge",
>> "some minor knowledge", and "deepened knowledge".
>> 
>> I use all of the 3 linked items as unique controls in a regression,
>> that is a dummy of each item and level. However,
>> this becomes tedious when interacting my treatment
>> variable with each of these items separately. Still
>> I do not feel very confident aggregating all three variables
>> since one item might be more relevant that the other.
> 
> The easiest solution would be to add those indicator variables. This
> is equivalent to constraining the effects of the three items to be the
> same, which in some cases makes sense and in others less so. Anyhow,
> it is a testable constraint. See:
> <http://www.maartenbuis.nl/publications/sum_constr.html>
> 
> If you think of these items as adding up to a total pool of knowledge
> on this issue and that total pool in turn influences whatever outcome
> variable you have, than you can look at:
> <http://www.maartenbuis.nl/wp/prop.html>
> 
> If you think that these items are influenced by some latent variable
> (probably knowledge) than you could look at (Hardouin et al. 2011).
> Notice that the distinction between this way of thinking and the
> previous one is that now the latent knowledge is influencing the
> observed items, while in the preceding way the observed items are
> influencing the latent pool of knowledge. Choosing between these two
> is just a matter of theory and substantive knowledge of the phenomenon
> being studied.
> 
> Hope this helps,
> Maarten
> 
> Jean-Benoit Hardouin, Angélique Bonnaud-Anti, Véronique Sébille (2011)
> "Nonparametric item response theory using Stata". The Stata Journal,
> 11(1):30-51.
> <http://www.stata-journal.com/article.html?article=st0216>
> 
> 
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
> 
> 
> http://www.maartenbuis.nl
> --------------------------
> 
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