A counting process is a stochastic process whose sample paths are
nondecreasing, right-continuous,
and nonnegative integer-valued, with
. It models a stream of events by
taking
to be the number that have occurred by time
. Thus, for
, the increment
counts the events occurring in the interval .
If every jump has size one, the jump times of a counting process define a simple point
process. Conversely, a locally finite simple temporal
point process on
with no point at 0 determines a counting process by counting
its points in the interval
for
(Daley and Vere-Jones 2003).