  The main technique that has been used to estimate the rate of gravitational
wave (gw) bursts is to search for coincidence among times of arrival of
candidate events in different detectors. Coincidences are modeled as a
(possibly non-stationary) random time series background with gw events embedded
in it, at random times but constant average rate. It is critical to test
whether the statistics of the coincidence counts is Poisson, because the counts
in a single detector often are not. At some point a number of parameters are
tuned to increase the chance of detection by reducing the expected background:
source direction, epoch vetoes based on sensitivity, goodness-of-fit
thresholds, etc. Therefore, the significance of the confidence intervals itself
has to be renormalized. This review is an insight of the state-of-the-art
methods employed in the recent search performed by the International
Gravitational Event Collaboration for the worldwide network of resonant bar
detectors.
