In case of Antioxidant study and determination of IC50, I think the slop equation (Y=mx+c or Y=mx-c) do not fully support. Say for example, my % inhibition values are 34.08, 57.83, 93.67, 97.43, 98.87 at 2, 5, 10, 20, and 50 ug of plant extract, respectively. Now if I put the values and draw the slop and follow the mentioned equation I will get either "-8.527" or "108.678" values. Do I believe this is correct? Correct me if I am wrong.