Test data from a 21 day fish test

Test data from a 21 day fish test following the guidelines OECD GL204, using the test organism Rainbow trout Oncorhynchus mykiss.

Usage

data(O.mykiss)

Format

A data frame with 70 observations on the following 2 variables.

conc: a numeric vector of concentrations (mg/l)
weight: a numeric vector of wet weights (g)

Details

Weights are measured after 28 days.

Source

Organisation for Economic Co-operation and Development (OECD) (2006) CURRENT APPROACHES IN THE STATISTICAL ANALYSIS OF ECOTOXICITY DATA: A GUIDANCE TO APPLICATION - ANNEXES, Paris (p. 65).

References

Organisation for Economic Co-operation and Development (OECD) (2006) CURRENT APPROACHES IN THE STATISTICAL ANALYSIS OF ECOTOXICITY DATA: A GUIDANCE TO APPLICATION - ANNEXES, Paris (pp. 80–85).

Examples

library(drc)

head(O.mykiss)
#>   conc weight
#> 1    0    2.8
#> 2    0    3.0
#> 3    0    2.7
#> 4    0    3.9
#> 5    0    3.1
#> 6    0    1.8

## Fitting exponential model
O.mykiss.m1 <- drm(weight ~ conc, data = O.mykiss, fct = EXD.2(), na.action = na.omit)
modelFit(O.mykiss.m1)
#> Lack-of-fit test
#> 
#>           ModelDf    RSS Df F value p value
#> ANOVA          54 17.620                   
#> DRC model      59 18.492  5  0.5351  0.7488
summary(O.mykiss.m1)
#> 
#> Model fitted: Exponential decay with lower limit at 0 (2 parms)
#> 
#> Parameter estimates:
#> 
#>                 Estimate Std. Error t-value   p-value    
#> d:(Intercept)   2.846794   0.092526 30.7674 < 2.2e-16 ***
#> e:(Intercept) 111.738614  33.196876  3.3659  0.001347 ** 
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#> 
#> Residual standard error:
#> 
#>  0.5598508 (59 degrees of freedom)

## Fitting same model with transform-both-sides approach
O.mykiss.m2 <- boxcox(O.mykiss.m1 , method = "anova")

summary(O.mykiss.m2)
#> 
#> Model fitted: Exponential decay with lower limit at 0 (2 parms)
#> 
#> Parameter estimates:
#> 
#>                 Estimate Std. Error t-value   p-value    
#> d:(Intercept)   2.841793   0.094431 30.0937 < 2.2e-16 ***
#> e:(Intercept) 104.115039  28.024151  3.7152  0.000453 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#> 
#> Residual standard error:
#> 
#>  0.4246342 (59 degrees of freedom)
#> 
#> Non-normality/heterogeneity adjustment through Box-Cox transformation
#> 
#> Estimated lambda: 0.707 
#> Confidence interval for lambda: [-0.0109, 1.5368] 
#> 
# no need for a transformation

## Plotting the fit
plot(O.mykiss.m1, type = "all", xlim = c(0, 500), ylim = c(0,4),
xlab = "Concentration (mg/l)", ylab = "Weight (g)", broken = TRUE)