The poisson effect

The Poisson effect relates to probability distribution of rare events, known as a Poisson distribution. In very small systems, the 1999 UARL equation assumes very small numbers of bursts per year. As system size reduces, the average number of UARL bursts fall and becomes more ‘skewed’, with a greater chance of fewer bursts in any one year than the arithmetic average. The median number of bursts (with 50% chance of occurrence in any year) is more representative than the average number over many years (which was used in the 1999 UARL equation) . However, as system size increases, the Poisson distribution becomes very similar to the ‘normal’ bell-shaped distribution, and the median and mean values become almost identical).