LW1949 (version 1.1.0)

LWestimate: Generate Litchfield and Wilcoxon Estimates

Description

Generate Litchfield and Wilcoxon's (1949) estimates in the evaluation of dose-effect experiments.

Usage

LWestimate(estParams, DEdata)

Arguments

estParams

A numeric vector of length 2, the estimated parameters (intercept and slope) of a straight line on the log10-probit scale, typically output from fitLWauto.

DEdata

A data frame of dose-effect data (typically, the output from dataprep) containing at least eight variables: dose, ntot, nfx, pfx, log10dose, bitpfx, fxcateg, and LWkeep (see Details).

Value

A list of length three:

• chi = the chi-squared statistic with associated P value and degrees of freedom,
• params = the estimated intercept and slope of the dose-response curve on the log10 probit scale,
• LWest = the Litchfield Wilcoxon estimates of ED50 with 95% confidence intervals and the number of records with partial effects (npartfx) as well as other metrics used in their step-by-step approach (ED16, ED84, S with 95% confidence intervals, N', and fED50).

Details

The input data are expected to be summarized by dose. If duplicate doses are provided, an error will be thrown.

References

Litchfield, JT Jr. and F Wilcoxon. 1949. A simplified method of evaluating dose-effect experiments. Journal of Pharmacology and Experimental Therapeutics 96(2):99-113. http://jpet.aspetjournals.org/content/96/2/99.abstract.

Examples

dose <- c(0.0625, 0.125, 0.25, 0.5, 1)
ntested <- rep(8, 5)
nalive <- c(1, 4, 4, 7, 8)
mydat <- dataprep(dose=dose, ntot=ntested, nfx=nalive)
mydat
intslope <- fitLWauto(mydat)
LWestimate(intslope, mydat)