[Rasch] One partial-credit item or multiple dichotomous items?

Mike Linacre mike at winsteps.com
Tue Mar 3 09:20:28 EST 2015


Thanks for the question, Stuart.

If you think of your item as a 2-stage adaptive test:

1. Did you understand? 0/1
2. If yes, how much? 0/1

Then the possibilities are
11
10
0(missing)

But your item is really a rating scale, because the decision about 
whether to choose "Did not understand at all" is influenced by the next 
level up "Understood incompletely". If the next level up had been 
"Understood almost nothing", then there would have been fewer people 
choosing "Did not understand at all", perhaps no one, because presumably 
everyone understood enough to read the words in the item.

OK?

Mike L.


On 3/3/2015 7:42 AM, Stuart Luppescu wrote:
> Hello Fellow Raschies, I'm working on a test with some partial-credit
> items. The coding is something like 0: Did not understand at all; 1:
> Understood incompletely; 2: Understood completely.
> I'm debating with the test developers about whether to make these
> individual items scored {0, 1, 2} or two dichotomous items: item 1:
> understood at least partially; item 2: understood completely. Is there
> an advantage to using one or the other approach?
> Also, if we go with the two-dichotomous-item approach, how should the
> second item be scored if the student did not understand the question at
> all? That is, does it make a difference if the two items are scored 0,
> 0; or 0, omitted?
>
> TIA.



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