[Rasch] Re: Rasch Digest, Vol 57, Issue 10

Hudson Golino hfgolino at gmail.com
Fri Apr 23 12:19:04 EST 2010


Sorry, I made a mistake:

> 1) Cross-plotted 24 item's measures, being 8 the same for both forms, plus
>
> the 16 less changed items;
>
> 2) Analyzed them in terms of the slope of the best fit line, obtaining a
>
> slope of 1.332;
>
> 3) I then removed the items whose measure differences between form B and
>
> form A where over 1.25, remaining with 11 items, with a slope equal to
>
> 1.128.
>
> *4) I've calculated the equating constant (x-axis' intercept)  and summed
it
>
> to form B item's measures. Then, I've examined the scatterplot (new form B
>
> Item's measure on Y-axis, and form A item's measures on X-axis), and find
>
> closed points with the best fit line, for all the 11 items.

*Considering the infit and outfit indexes of Form A and B, both can be
considered adequate. The reliability of persons where .95 and items .98 for
A form, and .95 and .99 for B form. The changes was made on items aiming to
produce considerable gaps between clusters of items.

Thanks again!


Hudson Golino
Assistant Researcher
Laboratory for Cognitive Architecture Mapping (LaiCo)
Federal University of Minas Gerais
Brazil


2010/4/22 <rasch-request at acer.edu.au>

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>   1. Doubt on Equating and Linking (Hudson Golino)
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> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 22 Apr 2010 22:51:50 -0300
> From: Hudson Golino <hfgolino at gmail.com>
> Subject: [Rasch] Doubt on Equating and Linking
> To: rasch at acer.edu.au
> Message-ID:
>        <t2w6ac9a0551004221851tc321da35p1156406362a9bae4 at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Dear colleagues,
>
> I've adopted an procedure, and I would like your opinion: Can it be
> considered a valid strategy?
>
> I have administered a 48 items test to a group of 167 people (Form A).
> After
> all the analysis, I changed the majority of items, for different, but
> relative ones (Form B), and administered it to a small group of 75 people.
> >From 48 items, just 8 remained the same. In spite of this rough test
> reformulation, the new items are closed-related to the old ones (same
> latent
> trait, same structure). Being a neo-piagetian like test, I have items
> ranging from earlier stages to higher stages. So, the 8 equal items are all
> from the earlier stages, the easiest ones.
>
> Aiming to equate and link both forms (A and B), I've adopted this "mixed"
> procedure:
>
> 1) Cross-plotted 24 item's measures, being 8 the same for both forms, plus
> the 16 less changed items;
> 2) Analyzed them in terms of the slope of the best fit line, obtaining a
> slope of 1.332;
> 3) I then removed the items whose measure differences between form B and
> form A where over 1.25, remaining with 11 items, with a slope equal to
> 1.128.
> 4) I've calculated the equating constant (x-axis' intercept)  and summed it
> to form B item's measures. Then, I've examined the scatterplot (new form B
> Item's measure on Y-axis, and form B item's measures on X-axis), and find
> closed points with the best fit line, for all the 11 items.
>
> Now, I just need to calculate the USCALE ( = the value of 1/slope) and the
> UMEAN ( = the value of the x-intercept) and reanalyze Test B.
>
>
> So, what do you think?
>
> It is a valid procedure?
>
>
> Thank you,
>
> Hudson Golino
> Assistant Researcher
> Laboratory for Cognitive Architecture Mapping (LaiCo)
> Federal University of Minas Gerais
> Brazil
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