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Pock Lesions on Chick Embryos

Keywords: overdispersion, quasi-likelihood, Poisson, negative-binomial

Description

A study was conducted concerning the counts of lesions produced on membranes of chick embryos by viruses of the pox group. The data give the numbers of lesions formed at a series of dilutions of the viral medium.


	Variable		Descriptions

	Dilution		Dilution of viral medium, from 1 to 32
	Count		Number of lesions

Download

Data File (tab-delimited text)

Source

Armitage, P. (1957). Studies in the variability of pock counts. Journal of Hygiene 55, 564-581.

Breslow, N. E. (1990). Further studies in the variability of pock counts. Statistics in Medicine 9, 615-626.

Faddy, M. J. (1997). Extended Poisson process modelling and analysis of count data. Biometrical Journal 39, 431-440.

Podlich, H. M., Faddy, M. J., and Smyth, G. K. (1999). Semi-parametric extended Poisson process models. Working Paper, Centre for Statistics, University of Queensland.

Analysis

The mean is approximately proportional the log-dilution. The data appear to be overdispersed relative to the Poisson distribution but underdispersed relative to the negative binomial distribution.