Hello everyone,

I am using the drc package to calculate and plot dose response curves. I recently tried to plot curves with control data (i.e. x values of 0), but doing so gives me problems with the x-axis.

Here is some example:

library(drc)

library(data.table)#x-axis data

dose <- c(0, 0, 0,

0.03, 0.03, 0.03,

0.08, 0.08, 0.08,

0.25, 0.25, 0.25,

0.75, 0.75, 0.75,

2, 2, 2,

6.67, 6.67, 6.67,

20, 20, 20)#y-axis data

resp <- c(120,122,125,

99,98,95,

100,97,98,

99,97,98,

83,86,85,

46,41,49,

1,2,3,

0,0,1

)#create data table with dose and response data

Data <- data.table(dose=dose, resp=resp)

#use drm function of drc package to get curve data (a drm object)

drm <- drm(resp ~ dose, data = Data, fct = llogistic2())plot(drm,

lwd = 5, #curve thickness

col = "blue", #curve color

broken = TRUE, #use breakpoint in x-axis

bp = min(dose[dose!=0]), #breakpoint is supposed to start at second biggest dose

type = 'average', #draw average resp for each unique dose

ylim = c(0, 150), #range of y-axis

cex.main = 2, #title size

cex.lab = 2, #lable size

cex.axis =2 #axis lable size

)

If I run this code, I get the following plot:

I would like to solve 3 issues:

- The x-axis tick after the axis break is not vertically aligned with the drawn response value (blue point above)
- I would like to add logarithmic ticks between the existing ticks, but without adding any further numbers on the axis.
- Is there a way to use the break and still have the curve starting from the control?

I already tried to achieve these by experimenting with drc.plot() and axis() parameters. Unfortunately, without any satisfying results. So it would be great, if someone can help me out!

Thank you,

Eike