  The event mixing method is analyzed for the study of the event-by-event
$K/\pi$ ratio distribution. It is shown that there exists some correlation
between the kaon and pion multiplicities in the mixed events. The $K/\pi$ ratio
distributions in the mixed events for different sets of real events are shown.
The dependence of the distributions on the mean $K/\pi$ ratio, mean and
variance of multiplicity distribution in the real events is investigated
systematically. The effect of imperfect particle identification on the $K/\pi$
ratio distribution in the mixed event is also considered.
