R: Example from Finney (1971)

finney71 {drc} | R Documentation

## Example from Finney (1971)

### Description

For each of six concentration of an insecticid the number of insects affected (out of the number of insects) was recorded.

### Usage

    data(finney71)

### Format

A data frame with 6 observations on the following 3 variables.

`dose`

  a numeric vector

`total`

  a numeric vector

`affected`

  a numeric vector

### Source

Finney, D. J. (1971) Probit Analysis, Cambridge: Cambridge University Press.

### Examples

    ## Model with ED50 as a parameter
    finney71.m1 <- drm(affected/total ~ dose, weights = total,
    data = finney71, fct = LL.2(), type = "binomial")

    summary(finney71.m1)
    plot(finney71.m1, broken = TRUE, bp = 0.1, lwd = 2)

    ED(finney71.m1, c(10, 20, 50), interval = "delta", reference = "control")

    ## Model fitted with 'glm'
    #fitl.glm <- glm(cbind(affected, total-affected) ~ log(dose),
    #family=binomial(link = logit), data=finney71[finney71$dose != 0, ])
    #summary(fitl.glm)  # p-value almost agree for the b parameter
    #
    #xp <- dose.p(fitl.glm, p=c(0.50, 0.90, 0.95))  # from MASS
    #xp.ci <- xp + attr(xp, "SE") %*% matrix(qnorm(1 - 0.05/2)*c(-1,1), nrow=1)
    #zp.est <- exp(cbind(xp.ci[,1],xp,xp.ci[,2]))
    #dimnames(zp.est)[[2]] <- c("zp.lcl","zp","zp.ucl")
    #zp.est  # not far from above results with 'ED'

    ## Model with log(ED50) as a parameter
    finney71.m2 <- drm(affected/total ~ dose, weights = total,
    data = finney71, fct = LL2.2(), type = "binomial")

    ## Confidence intervals based on back-transformation
    ##  complete agreement with results based on 'glm'
    ED(finney71.m2, c(10, 20, 50), interval = "fls", reference = "control")

[Package drc version 3.0-1 Index]