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PSYCHOLOGICAL SCIENCE Research Article
 

Summary: PSYCHOLOGICAL SCIENCE
Research Article
ON THE DANGERS OF AVERAGING ACROSS SUBJECTS
WHEN USING MULTIDIMENSIONAL SCALING OR THE
SIMILARITY-CHOICE MODEL
F. Gregory Ashby,' W. Todd Maddox,^ and W. William Lee'
'University of California at Santa Barbara and ^Arizona State University
Abstract--When ratings of judged similarity or frequencies of
stimulus identification are averaged across subjects, the psy-
chological structure ofthe data is fundamentally changed. Re-
gardless of the structure of the individual-subject data, the
averaged similarity data will likely be well fit by a standard
multidimensional scaling model, and the averaged identifica-
tion data will likely be wellfit by the similarity-choice model. In
fact, both models often provide excellentfits to averaged data,
even if they fail to fit the data of each individual subject. Thus,
a goodfit of either model to averaged data cannot be taken as
evidence that the model describes the psychological structure
that characterizes individual subjects. We hypothesize that
these effects are due to the increased symmetry that is a math-

  

Source: Ashby, F. Gregory - Department of Psychology, University of California at Santa Barbara

 

Collections: Biology and Medicine; Computer Technologies and Information Sciences