Posted by
Swank, Paul R on
Jan 09, 2007; 5:00pm
URL: http://spssx-discussion.165.s1.nabble.com/Treating-Ordinal-Data-as-Continuous-tp1073024p1073030.html
The problem is compounded when one thinks of measurement scales as all
or none, it's either ordinal or interval. However, win, place, and show
in a horse race is clearly more ordinal that IQ scores. For IQ scores,
it is clear that the difference between an IQ of 50 and an IQ of 75 is
perhaps greater than th difference between 75 and 100. On the other and,
the difference between an IQ of 100 and 101 is probably pretty similar
to the difference between 99 and 100. It all relies on the relation
between the scale values and the underlying construct. I think some
scales are closer to being interval than ordianl while for others, the
opposite is true. A lot has to do with how well the scale was
constructed.
Paul R. Swank, Ph.D. Professor
Director of Reseach
Children's Learning Institute
University of Texas Health Science Center-Houston
-----Original Message-----
From: SPSSX(r) Discussion [mailto:
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Laurie Petch
Sent: Tuesday, January 09, 2007 4:01 AM
To:
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Subject: Treating Ordinal Data as Continuous
Apologies, this is more of a statistical question, though it does have
an indirect bearing on SPSS. As subscribers to this list will know, in
psychology it is common practice to treat ordinal level data deriving
from rating scales as if they were continuous data and subjecting them
to inferential statistical analysis. The argument I have heard in favour
of doing this is that ordinal data behave much more like continuous data
when they are summed and averaged. I have not seen this argument in
writing, however, and would be grateful to anyone who can point me in
the direction of a relevant source.
Also, if anyone can suggest counter-arguments to this justification,
that would be great too. It just strikes me that a score of '120' as
opposed to '118' on an anxiety measure is data of a very different kind
than someone who is 120cm tall as opposed to 118cm.
To say that ordinal data behave like continuous data is surely rather
like saying that, since cheese 'behaves' more like butter when it is
heated, it's okay to use cheese instead of butter to make a cake?
Laurie
--------
Laurie Petch
Chartered Educational Psychologist (British Psychological Society)