Abstract
In multiple sclerosis (MS) the number of new enhancing lesions seen on monthly magnetic
resonance imaging (MRI) scans is the most widely used response variable in MRI-monitored
studies of experimental treatments. However, no statistical model has been proposed
to describe the distribution of the number of such lesions across MS patients. This
article briefly summarizes the statistical models for counted data. The negative binomial
(NB) model is proposed to fit the number of new enhancing lesions counted in a set
of 56 untreated MS patients followed for 9 months. It is shown that the large variability
present in this data set is better addressed by the NB model (residual deviance=66.6,
54 degrees of freedom) than by the Poisson model (residual deviance=1830.1, 55 degrees
of freedom). Applications of the parametrization of lesion counts are discussed, and
an example related to computer simulations for the sample size estimation is presented.
Keywords
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Article Info
Publication History
Accepted:
December 24,
1998
Received in revised form:
October 22,
1998
Received:
July 20,
1998
Identification
Copyright
© 1999 Elsevier Science B.V. Published by Elsevier Inc. All rights reserved.
