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Re: st: Transforming response scales


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Transforming response scales
Date   Thu, 18 Mar 2010 01:41:54 -0700 (PDT)

--- On Thu, 18/3/10, Clyde Schechter wrote:
> In a study, one of our measures is a 17-item questionnaire. 
> Each item has a discrete 4-point response scale, with
> response 1 anchored at "Not at all" and 4 anchored at
> "A great deal."  No descriptors were provided for the
> intermediate responses.
> 
> Unfortunately, the first 70 respondents received an
> incorrect version of the questionnaire where the response
> scale went from 1 to 6, with the same anchors at the
> extremes, and no descriptors for responses 2 through 5. 
> After the error was noted, the questionnaire was fixed, and
> the correct version has been administered to just under 400
> additional participants. 
> 
> The question is whether we can salvage the data from those
> first 70 respondents by transforming the 6-point response
> set onto the 4-point version.  

> Since these responses are ordinal in nature, and will be
> later analyzed by calculating mean item response for each
> respondent anyway

In that case I would not transform them to a four point 
scale, but just rescale the values of the first 70 
observations so that they range between 1 to 4:

replace x = 3/5*(x-1) + 1 in 1/70

This is consistent with the assumption you are already
intend on making by computing the mean of these item, which 
is that the distances between each adjesent category are
equal. 

Hope this helps,
Maarten


--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


      

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