1. Determination of toxic doses from log normal and log logistic models
Data need to be transformed (linearized): a sigmoidal curve must be converted into a straight line

2. Data transformation: Step 1 Change “Dose” axis to log scale

3. Step 2: Convert % response to logit

4. Step 3: Plot the regression line of log-transformed concentration or dose (X) vs. logit-transformed response (Y). Should yield straight line

5. Estimate LC50
Y=a+bX, where Y – transformed logit, X- lnC, b – slope of the line, a – intercept of the line
Note that transformed logit is not defined for 0% and 100% mortality, so omit those data
Calculate the transformed logit value for your target mortality (for 50% it is 5) = Y.
Calculate X=ln(LC50)=[Y-a]/b=[5-a]/b.
Calculate LC50=ex.