dose-response curve

R code of the ggplot2 example

library(ggplot2)
library(drc)

## Four-parameter log-logistic model of ryegrass root length against the
## concentration of ferulic acid; ED50, the dose that halves the response.
data(ryegrass)
model <- drm(rootl ~ conc, data = ryegrass, fct = LL.4())
ed50 <- ED(model, 50, display = FALSE)[1, "Estimate"]
curve <- data.frame(conc = exp(seq(log(0.5), log(30), length.out = 200)))
curve$rootl <- predict(model, newdata = curve)
## Zero cannot sit on a log axis: the control is drawn at 0.5 and labelled 0.
ryegrass$x <- pmax(ryegrass$conc, 0.5)

p <- ggplot(ryegrass, aes(x = x, y = rootl)) +
  geom_vline(xintercept = ed50, colour = "#535353", linewidth = 0.4, linetype = "dashed") +
  geom_line(data = curve, aes(x = conc), colour = "#9b2367", linewidth = 0.7) +
  geom_point(size = 1.6, alpha = 0.6, colour = "#535353") +
  annotate("text", x = ed50 * 1.1, y = 7.6, hjust = 0, size = 3, colour = "#535353",
           label = paste0("ED50 = ", format(round(ed50, 2), nsmall = 2), " mM")) +
  scale_x_log10(breaks = c(0.5, 1, 3, 10, 30), labels = c("0", "1", "3", "10", "30")) +
  scale_y_continuous(labels = lex_number, limits = c(0, NA), expand = expansion(mult = c(0, 0.05))) +
  labs(title = "Ferulic acid halves ryegrass root growth at about 3 mM",
       subtitle = "Root length against concentration, log-logistic fit with four parameters",
       x = "Ferulic acid (mM, log scale)", y = "Root length (cm)",
       caption = "Data: Inderjit et al. 2002, via the drc R package") +
  theme_lex_viz(grid = "y", arrows = "xy")