Fits a 1-inflated Zipf distribution.
oizipf(N = NULL, lpstr1 = "logitlink", lshape = "loglink", type.fitted = c("mean", "shape", "pobs1", "pstr1", "onempstr1"), ishape = NULL, gpstr1 = ppoints(8), gshape = exp((-3:3) / 4), zero = NULL)
For initial values.
The 1-inflated Zipf distribution is a mixture
distribution of the
distribution with some probability of obtaining a (structural) 1.
Thus there are two sources for obtaining the value 1.
This distribution is written here
in a way that retains a similar notation to the
zero-inflated Poisson, i.e., the
probability P[Y=1] involves another parameter phi.
This family function can handle multiple responses.
An object of class
The object is used by modelling functions such as
Under- or over-flow may occur if the data is ill-conditioned. Lots of data is needed to estimate the parameters accurately. Usually, probably the shape parameter is best modelled as intercept-only.
Thomas W. Yee
## Not run: odata <- data.frame(x2 = runif(nn <- 1000)) # Artificial data odata <- transform(odata, pstr1 = logitlink(-1 + x2, inverse = TRUE), myN = 10, shape = exp(-0.5)) odata <- transform(odata, y1 = roizipf(nn, N = myN, s = shape, pstr1 = pstr1)) with(odata, table(y1)) fit1 <- vglm(y1 ~ x2, oizipf(zero = "shape"), data = odata, trace = TRUE) coef(fit1, matrix = TRUE) ## End(Not run)
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