Home Contents Glossary Search Help

Poisson distribution
Previous Up Next

 

The Poisson distribution describes random events, for which the probability of success per trial is very small but where the number of trials is so large that there is still a reasonable rate of success.

The formula for the Poisson distribution (which can be derived from the binomial distribution - see Comparison of distributions) is

where r is the number observed and m is the mean value.

Choose values of m to see the change in the distribution shape P(r)

Note how P(r) becomes more symmetrical as m increases (»1).

variance of the Poisson distribution s2= m, standard deviation s= .

An example of a Poisson distribution is the way signals emerge from a detector monitoring radioactivity.

 

The University of Liverpool
© 1999, 2000 The University of Liverpool, Department of Physics

EPSRCProject funded by The Engineering and Physical Sciences Research Council

Materials Teaching Educational ResourcesWebsite developed and maintained by the MATTER Project