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Multidimensional Scaling of Nominal Data: The Recovery of Metric Information with Alscal

Published online by Cambridge University Press:  01 January 2025

Forrest W. Young*
Affiliation:
University of North Carolina at Chapel Hill
Cynthia H. Null
Affiliation:
College of William and Mary
*
Requests for reprints should be sent to Forrest Young, Psychometric Laboratory, University of North Carolina, Davie Hall 013-A, Chapel Hill, North Carolina 27514.

Abstract

Multidimensional scaling has recently been enhanced so that data defined at only the nominal level of measurement can be analyzed. The efficacy of ALSCAL, an individual differences multidimensional scaling program which can analyze data defined at the nominal, ordinal, interval and ratio levels of measurement, is the subject of this paper. A Monte Carlo study is presented which indicates that (a) if we know the correct level of measurement then ALSCAL can be used to recover the metric information presumed to underlie the data; and that (b) if we do not know the correct level of measurement then ALSCAL can be used to determine the correct level and to recover the underlying metric structure. This study also indicates, however, that with nominal data ALSCAL is quite likely to obtain solutions which are not globally optimal, and that in these cases the recovery of metric structure is quite poor. A second study is presented which isolates the potential cause of these problems and forms the basis for a suggested modification of the ALSCAL algorithm which should reduce the frequency of locally optimal solutions.

Type
Original Paper
Copyright
Copyright © 1978 The Psychometric Society

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References

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