Zigeom {VGAM}R Documentation

Zero-Inflated Geometric Distribution

Description

Density, and random generation for the zero-inflated geometric distribution with parameter pszero.

Usage

dzigeom(x, prob, pszero = 0, log = FALSE)
pzigeom(q, prob, pszero = 0)
qzigeom(p, prob, pszero = 0)
rzigeom(n, prob, pszero = 0)

Arguments

x, q

vector of quantiles.

p

vector of probabilities.

prob

see dgeom.

n

number of observations.

pszero

Probability of structural zero (ignoring the geometric distribution), called phi. The default value corresponds to the response having an ordinary geometric distribution.

log

Logical. Return the logarithm of the answer?

Details

The probability function of Y is 0 with probability phi, and geometric(prob) with probability 1-phi. Thus

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

where W is distributed geometric(prob).

Value

dzigeom gives the density, pzigeom gives the distribution function, qzigeom gives the quantile function, and rzigeom generates random deviates.

Note

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

Author(s)

Thomas W. Yee

See Also

zigeometric, dgeom.

Examples

prob = 0.5; pszero = 0.2; x = (-1):20
(ii = dzigeom(x, prob, pszero))
max(abs(cumsum(ii) - pzigeom(x, prob, pszero))) # Should be 0
table(rzigeom(1000, prob, pszero))

## Not run:  x = 0:10
barplot(rbind(dzigeom(x, prob, pszero), dgeom(x, prob)),
        beside = TRUE, col = c("blue","orange"),
        ylab = "P[Y = y]", xlab = "y", las = 1,
        main = paste("zigeometric(", prob, ", pszero = ", pszero,
                     ") (blue) vs",
                     " geometric(", prob, ") (orange)", sep = ""),
        names.arg = as.character(x)) 
## End(Not run)

[Package VGAM version 0.8-4 Index]