R: Hormesis in lettuce plants

lettuce {drc} | R Documentation

## Hormesis in lettuce plants

### Description

Data are from an experiment where isobutylalcohol was dissolved in a nutrient solution in which lettuce (Lactuca sativa) plants were grown. The plant biomass of the shoot was determined af 21 days.

### Usage

    data(lettuce)

### Format

A data frame with 14 observations on the following 2 variables.

conc

  a numeric vector of concentrations of isobutylalcohol (mg/l)

weight

  a numeric vector of biomass of shoot (g)

### Details

The data set illustrates hormesis, presence of a subtoxic stimulus at low concentrations.

### Source

van Ewijk, P. H. and Hoekstra, J. A. (1993) Calculation of the EC50 and its Confidence Interval When Subtoxic Stimulus Is Present, ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY, 25, 25–32.

### References

van Ewijk, P. H. and Hoekstra, J. A. (1994) Curvature Measures and Confidence Intervals for the Linear Logistic Model, Appl. Statist., 43, 477–487.

### Examples

    ## Look at data
    lettuce

    ## Monotonous dose-response model
    lettuce.m1 <- drm(weight~conc, data=lettuce, fct=LL.3())

    plot(lettuce.m1, broken = TRUE)

    ## Model fit in van Ewijk and Hoekstra (1994)
    lettuce.m2 <- drm(weight~conc, data=lettuce, fct=BC.4())
    modelFit(lettuce.m2)

    plot(lettuce.m2, add = TRUE, broken = TRUE, type = "none", lty = 2)

    ## Hormesis effect only slightly significant
    summary(lettuce.m2)

    ## Hormesis effect highly significant
    ##  compare with t-test for the "f" parameter in the summary output)
    anova(lettuce.m1, lettuce.m2)

[Package drc version 3.0-1 Index]