# Population Model

A population of people is comprised of “meta-groups.” Within a meta-group, all parameters such as hospitalization rate remain constant with the exception of contact level. For example, in modeling a university, possible meta-groups could be undergraduates, graduates, professional students, and faculty/staff. A meta-group contact matrix encodes how often these meta-groups come into contact with one another. Within each meta-group, there are multiple groups that represent varying contact levels.

The `simpar.groups.MetaGroup`

class allows one to specify a vector
of number of contacts across meta-groups as well as a vector indicating what
fraction of the meta-group population is in each of these groups.
Alternatively, this can be specified with a truncated Pareto distribution.
Given a shape parameter and truncation point , the
fraction of the meta-group population with contacts is
where is the probability density function of
the Pareto distribution. Note these values are normalized to sum to 1.

The interactions among individuals within the same meta-group is assumed to be
well-mixed in that the amount of interaction group has with group
is proportional to both groups contact levels and the fraction of the
population of group . Hence, it is not assumed that more social
people tend to interact with more social people and vice versa. Similarly,
while the meta-group contact matrix encodes how much contact takes place
between two meta-groups, the interaction between them is assumed to be
well-mixed with respect to the groups that comprise them. See
`simpar.groups.MetaGroup`

and `simpar.groups.Population`

for
more details.