| ZIP {gamlss.dist} | R Documentation |
The function ZIP defines the zero inflated Poisson distribution, a two parameter distribution, for a gamlss.family object to be used in GAMLSS fitting
using the function gamlss(). The functions dZIP, pZIP, qZIP and rZIP define the density, distribution function, quantile function
and random generation for the inflated poisson, ZIP(), distribution.
ZIP(mu.link = "log", sigma.link = "logit") dZIP(x, mu = 5, sigma = 0.1, log = FALSE) pZIP(q, mu = 5, sigma = 0.1, lower.tail = TRUE, log.p = FALSE) qZIP(p, mu = 5, sigma = 0.1, lower.tail = TRUE, log.p = FALSE) rZIP(n, mu = 5, sigma = 0.1)
mu.link |
defines the mu.link, with "log" link as the default for the mu parameter |
sigma.link |
defines the sigma.link, with "logit" link as the default for the sigma parameter which in this case is the probability at zero.
Other links are "probit" and "cloglog"'(complementary log-log) |
x |
vector of (non-negative integer) quantiles |
mu |
vector of positive means |
sigma |
vector of probabilities at zero |
p |
vector of probabilities |
q |
vector of quantiles |
n |
number of random values to return |
log, log.p |
logical; if TRUE, probabilities p are given as log(p) |
lower.tail |
logical; if TRUE (default), probabilities are P[X <= x], otherwise, P[X > x] |
Let Y=0 with probability σ and Y sim Po(μ) with probability (1-σ) the Y has a Zero inflated Poisson Distribution given by
sigma+(1-sigma)e^(-mu)
if (y=0)
f(y)=(1-sigma)e^-mu mu^y/y!
if (y>0) for y=0,1,...,.
returns a gamlss.family object which can be used to fit a zero inflated poisson distribution in the gamlss() function.
Mikis Stasinopoulos d.stasinopoulos@londonmet.ac.uk, Bob Rigby r.rigby@londonmet.ac.uk
Lambert, D. (1992), Zero-inflated Poisson Regression with an application to defects in Manufacturing, Technometrics, 34, pp 1-14.
Rigby, R. A. and Stasinopoulos D. M. (2005). Generalized additive models for location, scale and shape,(with discussion), Appl. Statist., 54, part 3, pp 507-554.
Stasinopoulos D. M., Rigby R.A. and Akantziliotou C. (2006) Instructions on how to use the GAMLSS package in R. Accompanying documentation in the current GAMLSS help files, (see also http://www.gamlss.com/).
Stasinopoulos D. M. Rigby R.A. (2007) Generalized additive models for location scale and shape (GAMLSS) in R. Journal of Statistical Software, Vol. 23, Issue 7, Dec 2007, http://www.jstatsoft.org/v23/i07.
ZIP()# gives information about the default links for the normal distribution # creating data and plotting them dat<-rZIP(1000, mu=5, sigma=.1) r <- barplot(table(dat), col='lightblue') # library(gamlss) # fit the distribution # mod1<-gamlss(dat~1, family=ZIP)# fits a constant for mu and sigma # fitted(mod1)[1] # fitted(mod1,"sigma")[1]