# varRatio: First order approximation to variance of y-ordinate to slope... In qra: Quantal Response Analysis for Dose-Mortality Data

## Description

In contexts where an LD99 estimate will be used as a data value in a further analysis step, the inverse of the variance may be used as a weight. The y-ordinate is for the link function transformed value of a specified mortality proportion, commonly 0.50, or 0.90, or 0.99

## Usage

 `1` ```varRatio(phat = 0.99, b, vv, link = "cloglog") ```

## Arguments

 `phat` Mortality proportion `b` Length 2 vector of intercept and slope `vv` Variance-covariance matrix for intercept and slope `link` Link function that transforms expected mortalities to the scale of the linear predictor

## Details

This function should only be used, in order to speed up calculations that use the function `fieller` (call `fieller` with (`type="Delta"`)), in a context where it is to be used many times, and where a check has been made that its use leads to confidence intervals that are a close approximation to those given with the default argument (`type="Fieller"`).

## Value

A vector, with elements

 `xhat` Estimate `var` Variance, calculated using the Delta method, See the help page for `fieller` for further details and references.

## Examples

 ```1 2 3 4 5``` ```redDel <- subset(qra::codling1988, Cultivar=="Red Delicious") redDel.glm <- glm(cbind(dead,total-dead)~ct, data=redDel, family=quasibinomial(link='cloglog')) vv <- summary(redDel.glm)\$cov.scaled qra::varRatio(0.99, b=coef(redDel.glm), vv=vv, link="cloglog") ```

qra documentation built on Oct. 29, 2021, 9:06 a.m.