Zinb {VGAM}R Documentation

Zero-Inflated Negative Binomial Distribution

Description

Density, distribution function, quantile function and random generation for the zero-inflated negative binomial distribution with parameter phi.

Usage

dzinb(x, phi, size, prob=NULL, munb=NULL, log=FALSE)
pzinb(q, phi, size, prob=NULL, munb=NULL)
qzinb(p, phi, size, prob=NULL, munb=NULL)
rzinb(n, phi, size, prob=NULL, munb=NULL)

Arguments

x, q vector of quantiles.
p vector of probabilities.
n number of observations. Must be a single positive integer.
size, prob, munb, log Arguments matching dnbinom. The argument munb corresponds to mu in dnbinom and has been renamed to emphasize the fact that it is the mean of the negative binomial component.
phi Probability of zero (ignoring the negative binomial distribution), called phi.

Details

The probability function of Y is 0 with probability phi, and a negative binomial distribution with probability 1-phi. Thus

P(Y=0) = phi + (1-phi) * P(W=0)

where W is distributed as a negative binomial distribution (see rnbinom.) See negbinomial, a VGAM family function, for the formula of the probability density function and other details of the negative binomial distribution.

Value

dzinb gives the density, pzinb gives the distribution function, qzinb gives the quantile function, and rzinb generates random deviates.

Note

The argument phi is recycled to the required length, and must have values which lie in the interval [0,1].

Author(s)

Thomas W. Yee

See Also

zinegbinomial, rnbinom, rzipois.

Examples

munb = 3; phi = 0.2; k = 10
x = 0:10
(i = dzinb(x, phi=phi, mu=munb, size=k))
cumsum(i) - pzinb(x, phi=phi, mu=munb, size=k)  # Should be 0s
table(rzinb(100, phi=phi, mu=munb, size=k))

table(qzinb(runif(1000), phi=phi, mu=munb, size=k))
round(dzinb(x, phi=phi, mu=munb, size=k) * 1000) # Should be similar

## Not run: 
barplot(rbind(dzinb(x, phi=phi, mu=munb, size=k),
              dnbinom(x, mu=munb, size=k)),
        beside = TRUE, col = c("blue","green"),
        main=paste("ZINB(mu=", munb, ", k=", k, ", phi=", phi,
                   ") (blue) vs negative binomial(mu=", munb,
                   ", k=", k, ") (green)", sep=""),
        names.arg = as.character(x))
## End(Not run)

[Package VGAM version 0.7-7 Index]