On the Comparison of PAR, DARMA, and INAR in Modeling Count Time Series Data
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Abstract
This study evaluates the forecasting and fitting performance of three advanced models—Poisson Autoregressive (PAR), Discrete Autoregressive Moving Average (DARMA), and Integer-Valued Autoregressive (INAR) for count time series data exhibiting complex features such as autocorrelation, overdispersion, and zero inflation. Both simulated and empirical datasets were analyzed, and model performance was assessed using Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), Root Mean Square Error (RMSE), and Mean Absolute Error (MAE). The results indicate that PAR models significantly outperform DARMA and INAR models, achieving substantially lower AIC (482.53 vs. >5,310,479) and RMSE (3,742 vs. 246,682), highlighting their robustness in handling periodic trends and autocorrelation. In contrast, standard Poisson regression performs poorly under overdispersion, with an AIC approaching 5.3 million, while zero-inflated datasets compromise error metrics such as MAPE due to division by zero. Although DARMA and INAR models perform comparably, they are less effective in capturing extreme fluctuations or sudden spikes. These findings emphasize the limitations of conventional models and point to the need for more flexible approaches, such as hybrid ZIP-INAR models or Bayesian methods, to effectively manage overdispersion and zero inflation. The study concludes with a practical recommendation to prioritize PAR models when modeling autocorrelated count data.
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References
Abbott, S., Robin, N., Hellewell, J., & Akira, E. (2020). On estimating the time-varying reproduction number of SARS-CoV-2 using national and sub-national case counts. Center for Mathematical Modelling of Infectious Diseases, London School of Hygiene & Tropical Medicine.
Akeyede, I., Bakari, H. R., & Muhammad, R. B. (2022). On robustness of ARIMA and ACP model to overdispersion in analysis of count. Journal of the Nigeria Statistical Association, 34, [page range].
Akeyede, I., Yahaya, W. B., & Adeleke, B. L. (2015). On forecast strength of some linear and nonlinear time series models for stationary data structure. American Journal of Mathematics and Statistics, 5(4), 163-177. https://doi.org/[insert DOI if available]
Johnson, N. L., Kemp, A. W., & Kotz, S. (2005). Univariate discrete distributions (3rd ed.). Wiley.
Martin, T. G., Wintle, B. A., Rhodes, J. R., Kuhnert, P. M., Field, S. A., Low-Choy, S. J., Tyre, A. J., & Possingham, H. P. (1998). Zero tolerance ecology: Improving ecological inference by modelling the source of zero observations. Ecology Letters, 8(11), 1235-1246. https://doi.org/10.1111/j.1461-0248.2005.00826.x
Ndwiga, J., Otieno, R., & Waititu, A. (2019). Zero-inflated models for overdispersed count data: A comparative analysis of hurdle and zero-inflated Poisson models. Journal of Statistical Computation and Simulation, 89(15), 2829-2845. https://doi.org/10.1080/00949655.2019.1636987
Saleh, A., Muhammad, I., & Rahman, A. (2021). Time series analysis of count data in epidemiological studies: Methods and applications. Journal of Applied Statistics, 48(5), 891-915. https://doi.org/10.1080/02664763.2020.1856364
Silva, M. E. (2015). Time series models for count data: Theory and applications [Doctoral dissertation, University of Lisbon]. Repositório da Universidade de Lisboa. http://hdl.handle.net/10451/19535
Tawiah, A. I. (2021). Time series modelling on overdispersion. Journal of Environmental and Public Health, Ghana.




















