Mortality of tobacco budworms
For three days, moths of the tobacco budworm (Heliothis virescens) were exposed to doses of the pyrethroid trans-cypermethrin.
data(H.virescens)
A data frame with 12 observations on the following 4 variables.
dosea numeric vector of dose values (μ g)
numdeada numeric vector of dead or knocked-down moths
totala numeric vector of total number of moths
sexa factor with levels F M denoting a grouping according to sex
In Venables and Ripley (2002), these data are analysed using a logistic regression with base-2 logarithm of dose as explanatory variable.
Venables, W. N. and Ripley, B. D (2002) Modern Applied Statistics with S, New York: Springer (fourth edition).
## 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))
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