Re: st: RE: Mean test in a Likert Scale

[Ulrich Kohler <kohler@wzb.eu>]

On 01.09.2012 18:32, Nick Cox wrote:
> My examples -- miles per gallon, price, weight -- all qualify as ratio scales.
>
> If I understand you correctly, your view is that transformations are
> illegitimate in statistics.
>
> Is that right?
No, that is not what I wanted to say. I wanted to say that each scale 
has a set of transformations that are "allowed"  in the sense
that they don't change the defining features of the scale  (whether its 
nominal, ordinal, etc.). You can use any
transformation that is allowed, but than you should use only those 
statistics, whose conclusions are robust against
that transformations. You can even use transformations that change the 
scale, but than you should use a statistic
that is robust against that transformation.




Nick On Sat, Sep 1, 2012 at 3:50 PM, Ulrich Kohler <kohler@wzb.eu> wrote:
> > Am Samstag, den 01.09.2012, 02:16 +0100 schrieb Nick Cox:
> > > But this objection is so strong that it rules out taking out means in
> > > most circumstances, not just for ordinal scales.
> > >
> > > It's clearly true that mean of transform is not transform of mean
> > > unless that transform is a linear function. The same argument would
> > > imply that means are invalid for measured variables (e.g. means of
> > > miles per gallon, weight, price in the auto data) because they are not
> > > equivariant under transformation. Both theory and practice tell us
> > > that means, geometric means, harmonic means, etc. can all make some
> > > sense for many measured variables. Poisson regression and generalised
> > > linear models all hinge on this.
> > Sorry but I disaggree here. For an intervall scale a transformation such
> > as the one that I used in my example are not allowed because it would
> > obvioulsy distroy the equal distance characteristic of subsequent
> > values. For an intervall scale only linear transformations are allowed
> > and therfore substantive conclusions taken from the mean are robust for
> > arbitrary _allowed_ transformation of the intervall scale.
> >
> > > There's also a big difference of viewpoint here. Measurement theory
> > > loves these arguments about arbitrary order-preserving
> > > transformations, but I don't think they make much sense to scientists
> > > who actually do measurements.
> >
> > But I don't think we -- that is me and you -- disaggree here. In way
> > that's what I wanted to say when I said that an ordinal scale could be
> > taken as kind of an "conventional" absolute scale in some instances.
> >
> >
> >
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