Jay Tanzman wrote:
>
> Jay Warner wrote:
> >
> > Jay Tanzman wrote:
> >
> > > I just got chewed out by my boss for modelling the means of some 7-point
> > > semantic differential scales. The scales were part of a written,
> > > self-administered questionnaire, and were laid out like this:
> > >
> > > Not stressful 1__ 2__ 3__ 4__ 5__ 6__ 7__ Very stressful
> > >
> > > So, why or why not is it kosher to model the means of scales like this?
> > >
> > > -Jay
>
> My boss's objection was that he believes "categorically" (sorry) that semantic
> differential scales are ordinal.
>
> > 1) Why do you think the scale is interval data, and not ordinal or
> > categorical?
>
> Why would anyone think it is ordinal and not interval? Most of the scales were
> measuring abstract, subjective constructs, such as empathy and satisfaction, for
> which there is no underlying physical or biological measurement. Why not, then,
> _define_ degree of empathy as the subjects' rating on a 1-to-7 scale?
>
Why not indeed?! Of course you can do this - and in fact you are doing
this. The question is really - what properties should this variable
possess in order that it is meaningful - that is, that it reflects
'reality' meaningfully. If it does not do this, then whatever
conclusions you come to about your variable are of no use whatsoever.
It is certainly true that your variable is ordinal. Is it more than
this? It is extremely unlikely that it is fully numeric (that is,
'interval') because the difference between 1 and 2 is unlikely to have
the same meaning as the difference between 4 and 5. You cannot simply
define these differences to be equal - you need your variable to reflect
reality! However, it is probable that the scale is 'reasonably numeric',
so the assumption that the variable is interval may be reasonable. But
this will be a model, using a number of assumptions - as all these
things are.
It is important that you recognise this modelling aspect of your data
definition.
Regards,
Alan
--
Alan McLean ([EMAIL PROTECTED])
Department of Econometrics and Business Statistics
Monash University, Caulfield Campus, Melbourne
Tel: +61 03 9903 2102 Fax: +61 03 9903 2007
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