Zinegbin: Zero-Inflated Negative Binomial Distribution

Description

Density, distribution function, quantile function and random generation for the zero-inflated negative binomial distribution with parameter pstr0.

Usage

dzinegbin(x, size, prob = NULL, munb = NULL, pstr0 = 0, log = FALSE)
pzinegbin(q, size, prob = NULL, munb = NULL, pstr0 = 0)
qzinegbin(p, size, prob = NULL, munb = NULL, pstr0 = 0)
rzinegbin(n, size, prob = NULL, munb = NULL, pstr0 = 0)

Arguments

x, q

vector of quantiles.

vector of probabilities.

Same as in runif.

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.

pstr0

Probability of structural zero (i.e., ignoring the negative binomial distribution), called $ϕ$ .

Value

dzinegbin gives the density, pzinegbin gives the distribution function, qzinegbin gives the quantile function, and rzinegbin generates random deviates.

Details

The probability function of $Y$ is 0 with probability $ϕ$ , and a negative binomial distribution with probability $1 - ϕ$ . Thus $P (Y = 0) = ϕ + (1 - ϕ) P (W = 0)$ 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.

Examples

Run this code

# NOT RUN {
munb <- 3; pstr0 <- 0.2; size <- k <- 10; x <- 0:10
(ii <- dzinegbin(x, pstr0 = pstr0, mu = munb, size = k))
max(abs(cumsum(ii) - pzinegbin(x, pstr0 = pstr0, mu = munb, size = k)))  # 0
table(rzinegbin(100, pstr0 = pstr0, mu = munb, size = k))

table(qzinegbin(runif(1000), pstr0 = pstr0, mu = munb, size = k))
round(dzinegbin(x, pstr0 = pstr0, mu = munb, size = k) * 1000)  # Should be similar

# }
# NOT RUN {
barplot(rbind(dzinegbin(x, pstr0 = pstr0, mu = munb, size = k),
                dnbinom(x, mu = munb, size = k)), las = 1,
        beside = TRUE, col = c("blue", "green"), ylab = "Probability",
        main = paste("ZINB(mu = ", munb, ", k = ", k, ", pstr0 = ", pstr0,
                   ") (blue) vs NB(mu = ", munb,
                   ", size = ", k, ") (green)", sep = ""),
        names.arg = as.character(x)) 
# }

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