[Rasch] Number of categories

Purya Baghaei puryabaghaei at gmail.com
Fri Jan 1 19:48:34 EST 2010

Dear colleagues,
In a Likert scale analysis with 5 points using Rasch RSM, the map
showed that most of the items are clustered at the lower end of the
scale and there are only two items at the top with many respondents
falling at the upper part of the scale where there are no items. Well,
the solution is to add some items to cover the gap
The other finding was that the distance between the last two
thresholds was more than 4 logits. Although this is within the
acceptable distance of 1.4 to 5 logits (Linacre, 1999) it’s still a
wide gap.
I was just wondering if increasing the number of categories from 5 to
say, 8 can solve the problem of lack of items at the upper part of the
scale. Because it seems that respondents are capable of distinguishing
more subtle levels of the construct at the upper end of the scale. Can
increasing the number of categories be a substitute for writing more

Purya Baghaei, Ph.D
English Department,
Islamic Azad University,
Ostad Yusofi Str.
Mashad, Iran.
Phone: +98 511 6634763

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