R: Mortality of tobacco budworms

H.virescens {drc} | R Documentation

## Mortality of tobacco budworms

### Description

For three days, moths of the tobacco budworm (Heliothis virescens) were exposed to doses of the pyrethroid trans-cypermethrin.

### Usage

    data(H.virescens)

### Format

A data frame with 12 observations on the following 4 variables.

`dose`

  a numeric vector of dose values (μ g)

`numdead`

  a numeric vector of dead or knocked-down moths

`total`

  a numeric vector of total number of moths

`sex`

  a factor with levels `F` `M` denoting a grouping according to sex

### Details

In Venables and Ripley (2002), these data are analysed using a logistic regression with base-2 logarithm of dose as explanatory variable.

### Source

Venables, W. N. and Ripley, B. D (2002) Modern Applied Statistics with S, New York: Springer (fourth edition).

### Examples

    ## Fitting dose-response model (log-logistic with common slope)
    Hv.m1 <- drm(numdead/total~dose, sex, weights = total, data = H.virescens, fct = LL.2(),
    pmodels = list(~ 1, ~ sex - 1), type = "binomial")
    summary(Hv.m1)

    ## Fitting the same model as in Venables and Riply (2002)
    Hv.m2 <- glm(cbind(numdead, total-numdead) ~ sex + I(log2(dose)) - 1, data = H.virescens,
    family = binomial)

    ## Comparing the fits
    logLik(Hv.m1)
    logLik(Hv.m2)

    ## Estimated ED values (matching those given in MASS)
    ED(Hv.m1, c(25, 50, 75))

[Package drc version 3.0-1 Index]