A couple of years ago on the list you suggested the possibility
on the list of using SPSS MDS to analyze multiple grids. I am trying to
use this package but I'm not sure whether I'm using it appropriately for
the data nor am I clear about some of the 'technical' procedures. Could I
bend your ear, and anyone else' with some questions to see if I'm on the
right track(or not!)
I have data from 40 12 x 12 single 'before' and 'after' grids of trainee
teachers - supplied elements, elicited constructs - who were asked to
construe psychology topics before/after a programme of study. I also have
a group of 10 'experts' to add to the comparisons. The data is / (ticks)
or x (crosses) and triadic. I'm looking to see if/how the clustering of
elements changes between individual's grids and between groups.
Query 1:
I have entered the raw data under MDS 'create distances from data'. As
far as I can see the data is nominal (either ticks = 1 or crosses = 0) but
there doesn't seem to be a 'nominal' option. My understanding of the SPSS
Professional Statistics book is that my raw data (actual example below)
1 1 0 1 1 0 0 0 1 1 1 1
1 1 1 0 1 1 1 1 0 1 1 1
0 0 1 1 1 0 1 1 0 0 1 1
1 0 1 1 1 1 1 1 0 0 1 1
1 1 0 0 0 0 0 0 1 0 1 1
1 0 0 1 1 0 1 1 0 0 0 0
0 1 0 0 0 0 1 0 0 1 1 0
1 0 0 1 1 0 0 1 1 0 0 1
1 0 1 0 0 1 1 1 0 1 0 0
1 0 1 1 1 1 0 1 1 1 0 0
1 1 0 1 1 1 1 1 1 1 0 1
1 0 0 1 1 0 0 1 0 0 0 0
is asymmetrical and row conditional but under the 'create distances from
data' this is not an option and offers only Ordinal(tied/untied?)
/symmetric/matrix. Am I missing something obvious here? I have tried to
cross reference with other sources to give me some clues. I confess to
not fully understanding S-stress (.22638/9), stress (.18833/4) and RSQ
(.76642/3)values (could be query 3!) but these are (as shown) almost
identical to those generated when I have put in the inter/element distances
(obtained from the OMNIGRID package).
Query 2:
I am unclear as to the procedure to be completed in order to get
Replicated MDS. I am using SPSS for Windows 95 and am not familiar with
the 'old' syntax.
Sorry if these are amazingly tedious questions (and I've got more where
these came from!), I'd like to continue with the real stuff and would
appreciate your expertise.
Thanks
Anne-Marie Dobing
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