predprobit function

Determine the Effective Dose from a Probit Regression Fit

Determine the effective dose for a specified percent effect from a fitted probit regression model.

predprobit(pct, pfit, alpha = 0.05, logbase = 10)

Arguments

• pct: A numeric scalar of the effect (as a percent) for which to estimate the effective dose.
• pfit: An object of class glm representing a probit regression fit to dose-effect data, typically the result of a call to fitprobit.
• alpha: A numeric scalar, the significance level used to generate 100*(1 - alpha)% confidence limits, default 0.05.
• logbase: A numeric or logical scalar, the base of the log transformation used for dose in pfit, default 10. Use logbase=FALSE, if the dose was not log transformed.

Returns

A numeric vector of length three, the effective dose and the lower and upper 100*(1 - alpha)% confidence limits.

Examples

toxdat <- data.frame(
 dose=c(0.05, 0.0625, 0.125, 0.25, 0.5, 1),
 ntot=rep(8, 6),
 nfx = c(0, 1, 4, 4, 6, 8))
myfit <- fitprobit(toxdat)
predprobit(50, myfit)