ecotox (version 1.3.0)

LC_logit: Lethal Concentration Logit

Description

Calculates lethal concentration (LC) and its fiducial confidence limits (CL) using a logit analysis according to Finney 1971, Wheeler et al. 2006, and Robertson et al. 2007.

Usage

LC_logit(formula, data, p = seq(1, 99, 1),
 weights = NULL, het_sig = NULL, conf_level = NULL)

Arguments

formula

an object of class 'formula' or one that can be coerced to that class): a symbolic description of the model to be fitted. The details of model specification are given under Details.

data

an optional data frame, list or environment (or object coercible by as.data.frame to a data frame) containing the variables in the model. If not found in data, the variables are taken from environment(formula), typically the environment from which LC is called.

p

Lethal Concentration (LC) values for given p, example will return a LC50 value if p equals 50. If more than one LC value wanted specify by creating a vector.

weights

vector of 'prior weights' to be used in the fitting process. Should be a numeric vector, if set to NULL weights will not be used.

het_sig

signficance level from person's goodness-of-fit test that is used to decide if a hetrogentiy factor is used. NULL is set to 0.15.

conf_level

Adjust confidence level as necessary or NULL set at 0.95.

Value

Returns a data frame with predicted LC for given p level, lower CL (LCL), upper CL (UCL), LCL and UCL distance away from LC (LCL_dis & UCL_dis; important for creating a plot), Pearson's goodness-of-fit test, slope, intercept, slope and intercept p values and standard error, and LC variance.

References

Finney, D.J., 1971. Probit Analysis, Cambridge University Press, Cambridge, England, ISBN: 052108041X

Wheeler, M.W., Park, R.M., and Bailey, A.J., 2006. Comparing median lethal concentration values using confidence interval overlap or ratio tests, Environ. Toxic. Chem. 25(5), 1441-1444.10.1897/05-320R.1

Robertson, J.L., Savin, N.E., Russell, R.M. and Preisler, H.K., 2007. Bioassays with arthropods. CRC press. ISBN: 9780849323317

Examples

# NOT RUN {
head(lampreytox)

# within the dataframe used, control dose, unless produced a value
# during experimentation, are removed from the dataframe,
# as glm cannot handle values of infinite. Other statistical programs
# make note of the control dose but do not include within analysis


#calculate LC50 and LC99 for May

m <- LC_logit((dead / total) ~ log10(dose), p = c(50, 99),
         weights = lampreytox[c(1:19), ]$total,
         data = lampreytox[c(1:19), ])

#view calculated LC50 and LC99 for seasonal toxicity of a pisicide,
#to lamprey in 2011

m

#dose-response curve can be plotted using 'ggplot2'

library(ggplot2)

p1 <- ggplot(data = lampreytox[c(1:19), ],
             aes(x = log10(dose), y = (dead / total))) +
  geom_point() +
  geom_smooth(method = "glm",
            method.args = list(family = binomial(link = "logit")),
            aes(weight = total), colour = "#FF0000", se = TRUE)

p1

#calculate LC50s and LC99s for multiple toxicity tests, June, August, and September

j <- LC_logit((dead / total) ~ log10(dose), p = c(50, 99),
        weights = lampreytox[c(20:38), ]$total,
        data = lampreytox[c(20:38), ])

a <- LC_logit((dead / total) ~ log10(dose), p = c(50, 99),
        weights = lampreytox[c(39:51), ]$total,
        data = lampreytox[c(39:51), ])

s <- LC_logit((dead / total) ~ log10(dose), p = c(50, 99),
        weights = lampreytox[c(52:64), ]$total,
        data = lampreytox[c(52:64), ])

#group results together in a dataframe to plot with 'ggplot2'

results <- rbind(m[, c(1, 3:8, 11)], j[,c(1, 3:8, 11)],
                 a[, c(1, 3:8, 11)], s[, c(1, 3:8, 11)])

results$month <- with(results, factor(c("May", "May", "June", "June",
                                        "August", "August", "September",
                                        "September"),
                                        levels = c("May", "June",
                                        "August", "September")))

p2 <- ggplot(data = results, aes(x = month, y = dose,
                             group = factor(p), fill = factor(p))) +
  geom_col(position = position_dodge(width = 0.9), colour = "#000000") +
  geom_errorbar(aes(ymin = (dose - LCL_dis), ymax = (dose + UCL_dis)),
                size = 0.4, width = 0.06,
                position = position_dodge(width = 0.9))

p2
# }