VGAM (version 0.9-4)

qvar: 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 TRUE then the quasi-variances are returned, else the square root of them, called quasi-standard errors.

...

Currently unused.

Value

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

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.

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 = FALSE)  # 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))

plotqvar(fit1, col = "green", lwd = 3, scol = "blue", slwd = 2, las = 1)