Kruskal's MDS results

I understand that the stress is a measure of how good the
algorithm managed to represent the ordinal distances between
items. And I also see why it's dependent on the number of
dimensions. 
I was hoping someone could tell me exactly what the formula
for the percentual stress is. To me it's not clear how this
metric is calculated.

Regards,
Dieter


Michael Denslow wrote:

Hi Dieter,

I'll take a shot at this. As I understand it, the

stress is telling

you how the ordination distances compare with

original

dissimilarities that you calculated.

It is a measure how well your ordination has done in

representing the

relationship of your sites. Note that the stress will

differ

depending on how many dimensions are used. I believe

the default is k

= 2 in isoMDS.

Hope this helps, Michael

Dear List,

I'm trying to interpret the results of the

Kruskal's Non-metric

Multidimensional Scaling algorithm (isoMDS, MASS

package).

The 'goodness of fit' is reported as "The final

stress achieved (in

percent)".

What does this mean exactly? I've tried to google

for an answer but

I've not come up with a definitive answer.

Regards, Dieter


-- Dieter Vanderelst PhD Student

Active Perception Lab University of Antwerp http://batbits.webnode.com/

Postal Address: Prinsstraat 13 B-2000 Antwerp

Belgium

Michael Denslow

Graduate Student I.W. Carpenter Jr. Herbarium [BOON]

Department of

Biology Appalachian State University Boone, North

Carolina U.S.A.

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