Poisson distribution

Terms from Statistics for HCI: Making Sense of Quantitative Data

This probability distribution is used when you have some sort of binary data (such as the toss of a coin, or whether a die rolls a 6), a fixed number of trials (say tossing the coin 10 times) and each trial is independent. The Poisson distribution gives the probability of getting a certain number of 'successes' (e.g. head in a coin toss). The Poisson distribution has two parameters, N (the number of trials) and p (the probability that a single trial is a 'success'). The probability of n successes is then Comb(N,n) pn (1-p)N-n, where Comb(N.n) is the number of combinations of n things out of N = N! / ( n! (N-n)! ). When N becomes large, the central portion of the Poisson distribution is approximately Normal.

Used on page 52