1. you plot your data efficacy vs concentration;
2. you ask your computer program to generate a curve (or you draw one in the
old fashioned way);
3. you find the 50% of the maximum efficacy on the Y;
4. then find the corresponding X!
5. done!
should be able to done in 1 sec in a program... i use Prism, used to use the
expensive WinNonLin during my phd....
