Functions for computing density and producing random samples from a zero-inflated Poisson probability distribution.
dzipois( x , p , lambda , log=FALSE )
rzipois( n , p , lambda )Integer values to compute densities or probabilies of
Probability of a zero from bernoulli process
Poisson rate parameter (mean)
If TRUE, returns log-probability instead of probability
These functions provide density and random number calculations for zero-inflated Poisson observations. This distribution is defined as a finite mixture of zeros and Poisson values, where p determines the weight of the pure zeros. As such, the probability of a zero is p + (1-p)exp(-lambda). And the probability of a non-zero value x is (1-p)lambda^x exp(-lambda)/x!.
dzipois does its calculations in a way meant to reduce numerical issues with probabilities close to 0 and 1. As a result, it's not very fast.