# ellipse.glm: Outline an approximate pairwise confidence region In ellipse: Functions for Drawing Ellipses and Ellipse-Like Confidence Regions

 ellipse.glm R Documentation

## Outline an approximate pairwise confidence region

### Description

This function produces the ellipsoidal outline of an approximate pairwise confidence region for a generalized linear model fit.

### Usage

```## S3 method for class 'glm'
ellipse(x, which = c(1, 2), level = 0.95, t, npoints = 100,
dispersion, ...)
```

### Arguments

 `x` The first argument should be a `glm` object, usually resulting from a call to `glm()`. `which` Which selects the pair of parameters to be plotted. The default is the first two. `level` The confidence level of the region. Default 95%. `t` The t statistic on the boundary of the ellipse. For Binomial or Poisson families, `sqrt(qchisq(level, 2))` is used; for other distributions, `sqrt(2*qf(level, 2, df))` where `df` is the residual degrees of freedom. `npoints` How many points to return in the ellipse. `dispersion` The value of dispersion to use. If specified, it is treated as fixed, and the chi-square limits for `t` are used. If missing, it is taken from `summary(x)`. `...` Other `ellipse.default` parameters may also be used.

### Details

The summary function is used to obtain the approximate covariance matrix of the fitted parameters, the dispersion estimate, and the degrees of freedom.

### Value

A matrix with columns named according to which to outline the confidence region.

`ellipse.default`

### Examples

```
## Dobson (1990) Page 93: Randomized Controlled Trial :

counts <- c(18,17,15,20,10,20,25,13,12)
outcome <- gl(3,1,9)
treatment <- gl(3,3)
glm.D93 <- glm(counts ~ outcome + treatment, family=poisson())

# Plot an approximate 95 % confidence region for the two Outcome parameters

plot(ellipse(glm.D93, which = c(2,3)), type = 'l')
points(glm.D93\$coefficients[2], glm.D93\$coefficients[3])
```

ellipse documentation built on June 1, 2022, 1:07 a.m.