Extensions of the SEIR model for the analysis of tailored social distancing and tracing approaches to cope with COVID-19.

In the context of the COVID-19 pandemic, governments worldwide face the challenge of designing tailored measures of epidemic control to provide reliable health protection while allowing societal and economic activity. In this paper, we propose an extension of the epidemiological SEIR model to enable a detailed analysis of commonly discussed tailored measures of epidemic control-among them group-specific protection and the use of tracing apps. We introduce groups into the SEIR model that may differ both in their underlying parameters as well as in their behavioral response to public health interventions. Moreover, we allow for different infectiousness parameters within and across groups, different asymptomatic, hospitalization, and lethality rates, as well as different take-up rates of tracing apps. We then examine predictions from these models for a variety of scenarios. Our results visualize the sharp trade-offs between different goals of epidemic control, namely a low death toll, avoiding overload of the health system, and a short duration of the epidemic. We show that a combination of tailored mechanisms, e.g., the protection of vulnerable groups together with a "trace & isolate" approach, can be effective in preventing a high death toll. Protection of vulnerable groups without further measures requires unrealistically strict isolation. A key insight is that high compliance is critical for the effectiveness of a "trace & isolate" approach. Our model allows to analyze the interplay of group-specific social distancing and tracing also beyond our case study in scenarios with a large number of groups reflecting, e.g., sectoral, regional, or age differentiation and group-specific behavioural responses.

Natural disasters and indicators of social cohesion.

Do adversarial environmental conditions create social cohesion? We provide new answers to this question by exploiting spatial and temporal variation in exposure to earthquakes across Chile. Using a variety of methods and controlling for a number of socio-economic variables, we find that exposure to earthquakes has a positive effect on several indicators of social cohesion. Social cohesion increases after a big earthquake and slowly erodes in periods where environmental conditions are less adverse. Our results contribute to the current debate on whether and how environmental conditions shape formal and informal institutions.

Computer games and prosocial behaviour.

We relate different self-reported measures of computer use to individuals' propensity to cooperate in the Prisoner's dilemma. The average cooperation rate is positively related to the self-reported amount participants spend playing computer games. None of the other computer time use variables (including time spent on social media, browsing internet, working etc.) are significantly related to cooperation rates.

On the evolution of coarse categories.

We compare the evolutionary fitness of different cultures (or populations), where we think of culture as partitioning a set of decision situations into categories of situations treated the same. Information about optimal behavior in each category is passed on via a process of noisy cultural transmission. We show that coarse partitions (distinguishing less situations) can provide higher evolutionary fitness even if there are no explicit costs to holding finer partitions.

Limited memory can be beneficial for the evolution of cooperation.

In this study we analyze the effect of working memory capacity on the evolution of cooperation and show a case in which societies with strongly limited memory achieve higher levels of cooperation than societies with larger memory. Agents in our evolutionary model are arranged on a network and interact in a prisoner's dilemma with their neighbors. They learn from their own experience and that of their neighbors in the network about the past behavior of others and use this information when making their choices. Each agent can only process information from her last h interactions. We show that if memory (h) is too short, cooperation does not emerge in the long run. A slight increase of memory length to around 5-10 periods, though, can lead to largely cooperative societies. Longer memory, on the other hand, is detrimental to cooperation in our model.

The evolution of function-valued traits for conditional cooperation.

In this paper we study the evolution of function-valued traits for cooperation in environments that display varying degrees of population viscosity. Traits measure an individual's intrinsic propensity to cooperate in a standard bilateral Prisoner's dilemma and can be increasing, decreasing or constant functions of the probability to interact with individuals of ones own genotype. We first analyse adaptation to homogenous environments (with constant degree of viscosity). Comparing environments characterized by different degrees of viscosity, we find that the relation between viscosity and the equilibrium type distribution is not monotone. In fact, it is possible that in fluid populations (no viscosity) there is more cooperation in equilibrium than in populations with intermediate degrees of viscosity. In a second step we analyse heterogenous environments (with varying degrees of viscosity). We find that under very weak assumptions on the distribution of the viscosity parameter strictly increasing functions are always selected and under some parameter constellations they are uniquely so.