A generalized model of social and biological contagion

We present a model of contagion that unifies and generalizes existing models of the spread of social influences and microorganismal infections. Our model incorporates individual memory of exposure to a contagious entity (e.g. a rumor or disease), variable magnitudes of exposure (dose sizes), and heterogeneity in the susceptibility of individuals. Through analysis and simulation, we examine in detail the case where individuals may recover from an infection and then immediately become susceptible again (analogous to the so-called SIS model). We identify three basic classes of contagion models which we call epidemic threshold, vanishing critical mass, and critical mass classes, where each class of models corresponds to different strategies for prevention or facilitation. We find that the conditions for a particular contagion model to belong to one of the these three classes depend only on memory length and the probabilities of being infected by one and two exposures, respectively. These parameters are in principle measurable for real contagious influences or entities, thus yielding empirical implications for our model. We also study the case where individuals attain permanent immunity once recovered, finding that epidemics inevitably die out but may be surprisingly persistent when individuals possess memory.     

Evidence from hunter-gatherer and subsistence agricultural populations for the universality of contagion sensitivity

The phenomenon of magical contagion – the unobserved passage of properties between entities that come into physical contact – was described by anthropologists over a century ago, yet questions remain about its origin, function, and universality. Contagion sensitivity, along with the emotion of disgust, has been proposed to be part of a biologically-evolved system designed to reduce exposure to pathogens by increasing the avoidance of “contaminated” objects. Yet this phenomenon has not been studied using systematic psychological comparison outside of industrialized populations. Here we document contagion sensitivity in two culturally, geographically, and economically distinct populations with little exposure to Western biomedicine and formal education: the Hadza hunter-gatherers of Tanzania and Tannese subsistence-agriculturalists of Vanuatu. In both populations, a majority of individuals rejected familiar and palatable foods when contaminating items touched the food but were subsequently removed. The Tannese children in our study showed a similar response, consistent with previous research with Western children. Our data support the proposal that contagion sensitivity is universal in human populations.     

Measurement of non-randomness in spatial distributions

The measurement of departure from randomness in spatial distributions has widespread application in ecological work. Several “indices of non-randomness” are compared with regard to their dependence on sample number, sample size and density. Criteria for the best choice of index for specific situations are discussed. A new coefficient C_x is proposed for use with positively contagious distributions and tests of significance are given. When C_x and another index (S²/m−1) are used for positive and negative contagion respectively, values ranging from −1 through 0 (random) to +1 are obtained, regardless of sample number, sample size or density.     

运动昆虫密度和疾病传染数量估计的两类模型

根据推导,得到用于运动昆虫密度和疾病接触传染数量估计的二维和三维空间模型．两类模型分别适用于爬行昆虫和飞行昆虫的种群密度估计．二维空间模型可用于描述昆虫疾病的接触传染数量,针对不同的用途,将两类基本模型进行了数种拓广.两类模型的建立,为运动昆虫的密度估计及疾病流行研究提供了重要的定量工具．