Abstract #301388

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JSM 2003 Abstract #301388
Activity Number: 378
Type: Contributed
Date/Time: Wednesday, August 6, 2003 : 12:00 PM to 1:50 PM
Sponsor: General Methodology
Abstract - #301388
Title: On Modeling Overdispersion and Underdispersion
Author(s): Evdokia Xekalaki*+
Companies: Athens University of Economics and Business
Address: 18, Spetson St., Athens, , 153 42, Greece
Keywords: overdispersion ; underdispersion ; contagion ; clustering ; heterogeneity ; methods of ascertainment
Abstract:

Very often, in connection with applications, data exhibit a variability that differs from that anticipated under the hypothesized model. Such discrepancies between the empirical and the nominal variance, known as overdispersion or underdispersion, can be interpreted to be induced by a failure of some of the basic assumptions of the model. In this paper, modeling such practical complications is discussed including estimation and hypothesis testing. A classification of the model assumption failures is made by the type of the inducing mechanism into two categories: failures caused by deviations from the hypothesized structure of the parent population and failures resulting in by the method of ascertainment. Examples of practical situations where overdispersed or underdispersed data frequently occur within each of these categories are given and estimation and hypothesis testing aspects are discussed.

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