Re: Treating Ordinal Data as Continuous

Posted by Robinson Aschoff on Jan 09, 2007; 11:29am
URL: http://spssx-discussion.165.s1.nabble.com/Treating-Ordinal-Data-as-Continuous-tp1073024p1073031.html

Hi Laurie,

it is my experience too that ordinal data is commonly treated as if it
were continuous in psychology. This is not uncontroversial, however. I
found this english paper with some further references to this topic:
http://opencontent.org/docs/parametric.pdf. I would argue that one has to
decide for each particular case if using parametric statistic analysis is
justified. At least, the scale should not obviously violate equidistance.
Further discussion ranks around the question how robust the envisaged
statistical test is against the violation of the interval scale
assumption. Some argue that e.g. an ANOVA (given sufficient N) is
sufficient robust aginst this violation. Others are more sceptical.

I also have a german book chapter about this topic I could send you in
case it is of any use for you.

Regards
Robinson
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"SPSSX(r) Discussion" <[hidden email]> wrote on 09.01.2007
11:00:37:

> 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)
>