R: Quasi-variances Extraction Function

qvar {VGAM} | R Documentation

## Quasi-variances Extraction Function

### Description

Takes a `rcim` fit of the appropriate format and returns either the quasi-variances or quasi-standard errors.

### Usage

    qvar(object, se = FALSE, ...)

### Arguments

`object` | A `rcim` object that has family function `uninormal` with the `explink` link. See below for an example.
`se` | Logical. If `FALSE` then the quasi-variances are returned, else the square root of them, called quasi-standard errors.
`...` | Currently unused.

### Details

This simple function is ad hoc and simply is equivalent to computing the quasi-variances by `diag(predict(fit1)[, c(TRUE, FALSE)]) / 2`. This function is for convenience only. Serious users of quasi-variances ought to understand why and how this function works.

### Value

A vector of quasi-variances or quasi-standard errors.

### Author(s)

T. W. Yee.

### See Also

`rcim`, `uninormal`, `explink`, `Qvar`, `ships`.

### Examples

    data("ships", package = "MASS")
    Shipmodel <- vglm(incidents ~ type + year + period,
                      quasipoissonff, offset = log(service),
                      data = ships, subset = (service > 0))

    # Easiest form of input
    fit1 <- rcim(Qvar(Shipmodel, "type"), uninormal("explink"), maxit = 99)
    qvar(fit1)             # Quasi-variances
    qvar(fit1, se = TRUE)  # Quasi-standard errors

    # Manually compute them:
    (quasiVar <- exp(diag(fitted(fit1))) / 2)                 # Version 1
    (quasiVar <- diag(predict(fit1)[, c(TRUE, FALSE)]) / 2)   # Version 2
    (quasiSE  <- sqrt(quasiVar))

    ## Not run:  qvplot(fit1, col = "green", lwd = 3, scol = "blue", slwd = 2, las = 1)

[Package VGAM version 1.0-3 Index]