Enter the logarithm of the concentration of the agonist into X. This equation is sometimes referred to as a five-parameter logistic equation, abbreviated 5PL.
To extend the model to handle curves that are not symmetrical, the Richards equation adds an additional parameter, S, which quantifies the asymmetry. This curve is symmetrical around its midpoint. It fits four parameters: the bottom and top plateaus of the curve, the EC50 (or IC50), and the slope factor (Hill slope). The standard dose-response curve is sometimes called the four-parameter logistic equation. Use a related equation when X values are concentrations or doses. This equation is used when X values are logarithms of doses or concentrations.
