Re: Generalised Procrustes Analysis and Grids?

Devi Jankowicz (
Wed, 6 May 98 20:57:29 +0100

Miguel Sottomayer writes:

>I introduce myself a few months ago saying that I was trying to apply pcp
>to the study of product (wine) choice perceptual maps and consumer's
>Well, I'm now starting to analyse data from about 60 grids ranging from 3
>to 25 constructs (ratings 1 to 7).
>Amonst other things I'm using Generalized Procrustes Analysis (GPA) as a
>way to reach "aggregated" perceptual maps for pre-defined groups of
>respondents (on the basis of several background variables) and doing
>so trying to identify different perceptual segments.
>Three major problems are allways coming to my mind:
>1 - How to validate the interpretation of the "aggregated constructs" or
>factors that are produced by GPA (a list of "real" constructs
>highly correlated with each factor is given by GPA and is the basis of
>my interpretation..);

What a fascinating topic for research!

I wish I knew about Generalized Procrustes Analysis: perhaps you might
give a brief description? Hopefully, though, it is capable of usefully
supplementing a content analysis of the constructs themselves? (Or
perhaps a content analysis forms part of it directly?)

What I have in mind is that a technique which deals only with ratings
will provide an outcome which, presumably, would state that the following
two constructs (with the ratings of 7 elements given):

Bland 3 5 7 2 1 5 6 4 Flavoursome
Cheap 3 5 7 2 1 5 6 4 Expensive

share so much variance that there _must_ be an underlying ("true"?)
construct to account for the ratings;

yet would do so with exactly the same credibility if the second construct
had been:

Mythical 3 5 7 2 1 5 6 4 Historical

Yet, may I assure you, the third construct is irrelevant to the way in
which I construe wines! Which makes one wonder about the credibility of
the "underlying" construct identified in the first instance.

My point being that one seeks an analysis of the meaning, as well as of
the ratings, to say anything about the similarity of constructs being
used. Perhaps your question (I've selected only the first of your list,
since I don't know enough to address the second two) relates to this

I'm not being a smart-arse here: I really don't know anything about
Generalized Procrustes Analysis and will freely confess that I need to
know more before making the above comments more than tentatively. Boorman
did some work on a problem similar to the one that I've addressed,
(surely an issue critical in PCP), and I've the glimmerings of an answer
in the present case, but need to know more about GPA first, along the
lines of "how does it handle _content_?"

Kind regards,