LWestimate function

Generate Litchfield and Wilcoxon Estimates

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

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).

Returns

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.

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)

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. [link].