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Modeling zero inflated count data Garden, Cheryl Ellen
Abstract
A natural approach to analyzing the effect of covariates on a count response variable is to use a Poisson regression model. A complication is that the counts are often more variable than can be explained by a Poisson model. This problem, referred to as overdispersion, has received a great deal of attention in recent literature and a number of variations on the Poisson regression model have been developed. As such, statistical consultants are faced with the difficult task of identifying which of these alternative models is best suited to their particular application. In this thesis, two applications where the data exhibit overdispersion are investigated. In the first application, two treatments for chronic urinary tract infections are compared. The response variable represents the number of resistant strains of bacteria cultured from rectal swabs. In the second application, the number of units sold of a product are modeled as depending on two factors representing the day of the week and the store. Two alternative models that allow for overdispersion are used in both applications. The negative binomial regression model and the zero inflated Poisson regression model so named by Lambert (Lambert, 1992) provide improved fits. Further, the zero inflated Poisson regression model performs particularly well in the situation when the overdispersion is suspected to be due to a large number of zeroes occurring in the data. The zero inflated Poisson regression model allows one to both fit the data well and make some inference regarding the nature of the overdispersion present. This little known model may prove to be valuable as there exist a number of applications where observed overdispersion in a count response variable is clearly due to an inflated number of zeroes.
Item Metadata
Title |
Modeling zero inflated count data
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1996
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Description |
A natural approach to analyzing the effect of covariates on a count response variable is to
use a Poisson regression model. A complication is that the counts are often more variable than
can be explained by a Poisson model. This problem, referred to as overdispersion, has received a
great deal of attention in recent literature and a number of variations on the Poisson regression
model have been developed. As such, statistical consultants are faced with the difficult task of
identifying which of these alternative models is best suited to their particular application. In this
thesis, two applications where the data exhibit overdispersion are investigated. In the first
application, two treatments for chronic urinary tract infections are compared. The response
variable represents the number of resistant strains of bacteria cultured from rectal swabs. In the
second application, the number of units sold of a product are modeled as depending on two
factors representing the day of the week and the store.
Two alternative models that allow for overdispersion are used in both applications. The
negative binomial regression model and the zero inflated Poisson regression model so named by
Lambert (Lambert, 1992) provide improved fits. Further, the zero inflated Poisson regression
model performs particularly well in the situation when the overdispersion is suspected to be due
to a large number of zeroes occurring in the data. The zero inflated Poisson regression model
allows one to both fit the data well and make some inference regarding the nature of the
overdispersion present. This little known model may prove to be valuable as there exist a
number of applications where observed overdispersion in a count response variable is clearly due
to an inflated number of zeroes.
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Extent |
3575052 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-02-11
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0099036
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1996-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.