Transcription of Poisson Models for Count Data
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Chapter 4 Poisson Models for CountDataIn this chapter we study log-linear Models for Count data under the assump-tion of a Poisson error structure. These Models have many applications, notonly to the analysis of counts of events, but also in the context of Models forcontingency tables and the analysis of survival Introduction to Poisson RegressionAs usual, we start by introducing an example that will serve to illustrativeregression Models for Count data. We then introduce the Poisson distributionand discuss the rationale for modeling the logarithm of the mean as a linearfunction of observed covariates. The result is a generalized linear model withPoisson response and link The Children Ever Born DataTable , adapted from Little (1978), comes from the Fiji Fertility Surveyand is typical of the sort of table published in the reports of the WorldFertility Survey.
tween the mean and the variance. We will stress this point when we discuss our example, where the assumptions of a limiting binomial or a Poisson pro-cess are not particularly realistic, but the Poisson model captures very well the fact that, as is often the case with count data, the variance tends to increase with the mean.
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