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Latent trait modelling of symptoms of schizophrenia

Published online by Cambridge University Press:  09 July 2009

R. C. Bell ,
L. H. Low ,
H. J. Jackson ,
P. L. Dudgeon ,
D. L. Copolov  and
B. S. Singh
R. C. Bell*
Affiliation:
NH & MRC Schizophrenia Unit, Mental Health Research Institute of Victoria, Australia
L. H. Low
Affiliation:
NH & MRC Schizophrenia Unit, Mental Health Research Institute of Victoria, Australia
H. J. Jackson
Affiliation:
NH & MRC Schizophrenia Unit, Mental Health Research Institute of Victoria, Australia
P. L. Dudgeon
Affiliation:
NH & MRC Schizophrenia Unit, Mental Health Research Institute of Victoria, Australia
D. L. Copolov
Affiliation:
NH & MRC Schizophrenia Unit, Mental Health Research Institute of Victoria, Australia
B. S. Singh
Affiliation:
NH & MRC Schizophrenia Unit, Mental Health Research Institute of Victoria, Australia
*
1 Address for correspondence: Dr Richard C. Bell, Mental Health Research Institute of Victoria, Private Bag 3, Parkville, VIC 3052, Australia
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Synopsis

Latent trait models were fitted to data for 149 schizophrenic or schizophreniform in-patients rated on the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS) using the Rasch Extended Logistic Model. It was found that a reduction in the numbers of rating categories, from six to three or four led to consistencies in response while deletion of several items led to consistent scales of symptoms that accorded with an item response characterization. Behaviours included in the final scales varied in the numbers of categories, and in the range of symptom level covered by a category. Relationships between scores representing symptoms were found to be modelled better by a factor structure that included a third overlapping ‘cognitive’ factor in addition to the now traditional positive and negative factors, than by the original positive and negative factors alone.

Type
Original Articles
Information
Psychological Medicine , Volume 24 , Issue 2 , May 1994 , pp. 335 - 345
Copyright
Copyright © Cambridge University Press 1994

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