Semiparametric integer‐valued autoregressive models on ℤ

Abstract

In the analysis of real integer‐valued time series data, we often encounter negative values and negative correlations. For integer‐valued autoregressive time series, there are many parametric models to choose from, but some of them are relatively complex. With little information about the background of real data, we hope that a simple and effective semiparametric model can be used to obtain more information that usually cannot be provided by parametric models, such as the confidence interval of the innovation distribution. But the only existing semiparametric model based on thinning operators can only deal with non‐negative data with positive correlation coefficients. In addition, it has two drawbacks: first, an initial distribution of the innovation is required, but different initial values may lead to different results; second, the confidence interval of the innovation distribution is not available, which is essential in low‐valued data. To overcome these drawbacks, we propose a rounded semiparametric autoregressive model with a log‐concave innovation, which can deal with ‐valued time series with autoregressive coefficients of arbitrary sign. The consistencies of the estimators for the parametric and nonparametric parts of the model are also discussed. We illustrate the superior performance of the proposed model based on three real datasets.