LD₅₀

In Module 1, Cheech did an LD50 experiment. His was easy, because he had an experiment that returned 5 fish sick out of 10, which is 50% and the LD50 (or ED50) is direct. Here it is again:

And a graph

Note LD50 (or ED50) is a straightforward concept, if we are dealing with with quantal data, that is, an "all or nothing" response. Suppose we had a graded response. For example, "body weight at the end of three months." For each dose, there would be a range of responses. So one could have a mean and standard deviation for each dose. NEXT