Demographics files are JSON-formatted files that contain information on the demographics of the population in each node in the simulation. For example, the longitude and latitude, the number of individuals, and the distribution for age, gender, immunity, risk, and mortality. Once you have it configured for a given population and location, you will likely reuse it across many different simulation scenarios.
In addition, demographics files are useful for creating heterogeneity a population. You can define values for accessibility, age bins, geography, risk, and other properties and assign values to individuals or nodes. For example, you might want to divide a population up into different bins based on age so you can target interventions to individuals in a particular age range. Another common use is to configure treatment coverage to be higher for individuals in easily accessible regions and lower for individuals in areas that are difficult to access. for more information, see Individual and node properties.
You can also simulate a complex health care system using property values that represent the intervention status for each individual. For example, consider a disease that has a second-line treatment that is not used unless the first-line treatment has proven ineffective. You can assign a property value after receiving the first-line treatment and prevent anyone from receiving the second-line treatment unless they have that property value and are still symptomatic. For more information, see Cascade of care.
EMOD assumes homogeneous mixing and disease transmission for the generic simulation type. Using the individual properties in the demographics file, you can also use the HINT feature to add heterogeneous transmission to your generic model. You cannot manually configure heterogeneous transmission using HINT with other simulation types because the heterogeneity in transmission for specific diseases and disease classes is configured by transmission parameters specific to each disease model. For more information, see Property-based heterogeneous disease transmission.
You do have the option to run a simulation without a demographics file if you set Enable_Demographics_Builtin to 1 in the configuration file. However, this option is primarily used for software testing. It will not provide meaningful simulation data as it does not represent the population of a real geographic location.
The demographics file structure and parameters are described in more detail in Demographics parameters.