  Temporal social networks of human interactions are preponderant in
understanding the fundamental patterns of human behavior. In these networks,
interactions occur locally between individuals (i.e., nodes) who connect with
each other at different times, culminating into a complex system-wide web that
has a dynamic composition. Dynamic behavior in networks occurs not only locally
but also at the global level, as systems expand or shrink due either to:
changes in the size of node population or variations in the chance of a
connection between two nodes. Here, we propose a numerical maximum-likelihood
method to estimate population size and the probability of two nodes connecting
at any given point in time. An advantage of the method is that it relies only
on aggregate quantities, which are easy to access and free from privacy issues.
Our approach enables us to identify the simultaneous (rather than the
asynchronous) contribution of each mechanism in the densification and
sparsification of human contacts, providing a better understanding of how
humans collectively construct and deconstruct social networks.
