Let’s create an example. We will use the service model – when a customer joins your service, we consider that a birth, and when a customer leaves your service, that is a death. We have a record of all births, but at points in time we do not necessarily see all the deaths. Consider the graphic below. Each line represents a user moving through time. For each user, we of course observe their birth (joins service). At current time t, we only observesome deaths, denoted by red points, whereas the still active users have not suffered this death event yet.
See on blog.yhathq.com