Fundamentally, the population network can be considered a multilayer network with the following qualities:
- Nodes are people, with attributes like age.
- Edges represent interactions between people, with attributes like the setting in which the interactions take place (for example, household, school, or work). The relationship between the interaction setting and properties governing disease transmission, such as frequency of contact and risk associated with each contact, is mapped separately by Covasim or other agent-based model. SynthPops reports whether the edge exists or not.
If you are using SynthPops with Covasim, note that the relevant value in Covasim is the parameter beta, which captures the probability of transmission via a given edge per time step. The value of this parameter captures both number of effective contacts for disease transmission and transmission probability per contact.
The generated network is a multilayer network in the sense that it is possible for people to be connected by multiple edges each in different layers of the network. The layers are referred to as contact layers. For example, the workplace contact layer is a representation of all of the pairwise connections between people at work, and the household contact layer represents the pairwise connections between household members. Typically these networks are clustered; in other words, everyone within a household interacts with each other, but not with other households. However, they may interact with members of other households via their school or workplace. Some level of community contacts outside of these networks can be configured using Covasim or other model being used with SynthPops.
SynthPops functions in two stages:
- Generate people living in households, and then assign individuals to workplaces and schools.
Save the output to a cache file on disk. Implemented in
- Load the cached file and produce a dictionary that can be used by Covasim. Implemented in
make_population(). Covasim assigns community contacts at random on a daily basis to reflect the random and stochastic aspect of contacts in many public spaces, such as shopping centers, parks, and community centers.