Poliomyelitis cases reported to the U.S. Centers for Disease Control for the years 1970 to 1983, that is, 168 observations.

`data(polio)`

The format is: Time-Series [1:168] from 1970 to 1984: 0 1 0 0 1 3 9 2 3 5 ...

The data were originally modelled by Zeger (1988) who used a parameter driven approach, in which a first order autoregressive model was used for the latent process, to conclude that there is evidence of a decrease in the polio infection rate. The data were analysed also by Li (1994), Zeger and Qaqish (1988), Davis et al. (1999), and by Benjamin et al (2003).

Benjamin M. A., Rigby R. A. and Stasinopoulos D.M. (2003) Generalised Autoregressive Moving Average Models. *J. Am. Statist. Ass.*, 98, 214-223.

Davis, R. A., Dunsmuir, W. T. M. and Wang, Y. (1999), ``Modelling
Time Series of Count Data,'' *in Asymptotics, Nonparametrics
and Time Series (ed Subir Ghosh)*: Marcel Dekker

Zeger, S. L. (1988), ``A Regression Model for Time Series of
Counts,'' *Biometrika*, 75, 822-835.

Zeger, S. L. and Qaqish, B. (1988), ``Markov Regression Models
for Time Series: A Quasi-likelihood Approach,'' *Biometrics*,
44, 1019-1032.