zoabetaR {VGAM} | R Documentation

## Zero- and One-Inflated Beta Distribution Family Function

### Description

Estimation of the shape parameters of the two-parameter beta distribution plus the probabilities of a 0 and/or a 1.

### Usage

    zoabetaR(lshape1 = "loglink", lshape2 = "loglink", lpobs0 = "logitlink",
       lpobs1 = "logitlink", ishape1 = NULL, ishape2 = NULL, trim = 0.05,
       type.fitted = c("mean", "pobs0", "pobs1", "beta.mean"),
       parallel.shape = FALSE, parallel.pobs = FALSE, zero = NULL)

### Arguments

`lshape1, lshape2, lpobs0, lpobs1` | Details at `CommonVGAMffArguments`. See `Links` for more choices.
`ishape1, ishape2` | Details at `CommonVGAMffArguments`.
`trim, zero` | Same as `betaR`.
`parallel.shape, parallel.pobs` | See `CommonVGAMffArguments` for more information.
`type.fitted` | The choice `"beta.mean"` mean to return the mean of the beta distribution; the 0s and 1s are ignored. See `CommonVGAMffArguments` for more information.

### Details

The standard 2-parameter beta distribution has a support on (0,1), however, many datasets have 0 and/or 1 values too. This family function handles 0s and 1s (at least one of them must be present) in the data set by modelling the probability of a 0 by a logistic regression (default link is the logit), and similarly for the probability of a 1. The remaining proportion, `1-pobs0-pobs1`, of the data comes from a standard beta distribution. This family function therefore extends `betaR`. One has M=3 or M=4 per response. Multiple responses are allowed.

### Value

Similar to `betaR`.

### Author(s)

Thomas W. Yee and Xiangjie Xue.

### See Also

`Zoabeta`, `betaR`, `betaff`, `Beta`, `zipoisson`.

### Examples

    nn <- 1000; set.seed(1)
    bdata <- data.frame(x2 = runif(nn))
    bdata <- transform(bdata,
      pobs0 = logitlink(-2 + x2, inverse = TRUE),
      pobs1 = logitlink(-2 + x2, inverse = TRUE))
    bdata <- transform(bdata,
      y1 = rzoabeta(nn, shape1 = exp(1 + x2), shape2 = exp(2 - x2),
                    pobs0 = pobs0, pobs1 = pobs1))
    summary(bdata)
    fit1 <- vglm(y1 ~ x2, zoabetaR(parallel.pobs = TRUE),
                 data = bdata, trace = TRUE)
    coef(fit1, matrix = TRUE)
    summary(fit1)

[Package VGAM version 1.1-1 Index]