LWestimate: Generate Litchfield and Wilcoxon Estimates

In LW1949: An Automated Approach to Evaluating Dose-Effect Experiments Following Litchfield and Wilcoxon (1949)

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).

Details

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

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).

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].

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)

Example output

Warning message:
no DISPLAY variable so Tk is not available 
    dose ntot nfx rec   pfx log10dose    bitpfx fxcateg LWkeep
1 0.0625    8   1   1 0.125  -1.20412 -1.150349      50   TRUE
2 0.1250    8   4   2 0.500  -0.90309  0.000000      50   TRUE
3 0.2500    8   4   3 0.500  -0.60206  0.000000      50   TRUE
4 0.5000    8   7   4 0.875  -0.30103  1.150349      50   TRUE
5 1.0000    8   8   5 1.000   0.00000       Inf     100   TRUE
$chi
$chi$chi
  chistat        df      pval 
1.0168540 3.0000000 0.7971739 

$chi$contrib
           exp   obscorr    contrib
[1,] 0.1540923 0.1250000 0.04394056
[2,] 0.3697344 0.5000000 0.36716385
[3,] 0.6383023 0.5000000 0.42306128
[4,] 0.8509244 0.8750000 0.03110550
[5,] 0.9579061 0.9861477 0.15158280


$params
Intercept     Slope 
 1.726888  2.280443 

$LWest
       ED50       lower       upper     npartfx        ED16        ED84 
 0.17487995  0.08724768  0.35053078  4.00000000  0.06407062  0.47733260 
          S      lowerS      upperS      Nprime       fED50          fS 
 2.72948727  1.22640811  6.07473213 16.00000000  2.00440807  2.22559461 

LW1949 documentation built on May 2, 2019, 6:11 a.m.