Kanjilal P P, Bhattacharya J
Department of Electronics & ECE, Indian Institute of Technology, Kharagpur, 721302, India.
J Theor Biol. 1999 Mar 21;197(2):163-74. doi: 10.1006/jtbi.1998.0865.
The question addressed is whether or not childhood epidemics such as measles and chickenpox are characterized by low-dimensional chaos. We propose a new method for the detection and extraction of hidden periodic components embedded in an irregular cyclical series, and study the characterization of the epidemiological series in terms of the characteristic features or periodicity attributes of the extracted components. It is shown that the measles series possesses two periodic components each having a period of one year. Both the periodic components have time-varying pattern, and the process is nonlinear and deterministic; there is no evidence of strong chaoticity in the measles dynamics. The chickenpox series has one seasonal component with stable pattern, and the process is deterministic but linear, and hence non-chaotic. We also propose surrogate generators based on null hypotheses relating to the variability of the periodicity attributes to analyse the dynamics in the epidemic series. The process dynamics is also studied using seasonally forced SEIR epidemic model, and the characterization performance of the proposed schemes is assessed.
所探讨的问题是，诸如麻疹和水痘等儿童期流行病是否具有低维混沌特征。我们提出了一种新方法，用于检测和提取嵌入不规则周期性序列中的隐藏周期性成分，并根据提取成分的特征或周期性属性来研究流行病学序列的特征。结果表明，麻疹序列具有两个周期成分，每个周期为一年。这两个周期成分都具有随时间变化的模式，且该过程是非线性的和确定性的；在麻疹动态中没有强混沌性的证据。水痘序列有一个模式稳定的季节性成分，且该过程是确定性的但为线性的，因此是非混沌的。我们还基于与周期性属性变异性相关的零假设提出了替代生成器，以分析流行病序列中的动态。还使用季节性强迫的SEIR流行病模型研究了过程动态，并评估了所提方案的特征描述性能。
