LD50 and LT50 calculation

[#1]

Hi everybody,

I would want to calculate LD50 and LT50 from a dataset organized in 6 columns:

- Name of the compound (I just got 1 compound named A)

- Concentration of the compound (2 dilutions per compound)

- Individual number (a fixed number of 10 individuals is used per assay)

- State of the individual at the end of the experiment (1 = alive, 0 = dead)

- Day death (experiment last 15 days)

- Experiment number (2 replicates of the same experiment)

I drawn kaplan-meyer survival curves (y = day death, censor = state at the end of the experiment). Now I would want to calculate LD50 and LT50 using probit regression but I don't know how to process, could someone help me ?

Thanks by advance,

Cécilia