Fig. 1.

Normalized isoboles at 50% effect level, for the Bliss independence model, Eq. (2), for various values of γ₁ and γ₂, which are listed next to each corresponding curve. A single γ indicates that γ₁ = γ₂ = γ. When Hill coefficients are different (one larger than) 1.3 and the other less than 1.2), the isoboles are S-shaped and may cross the Loewe additivity diagonal line. The solid diagonal line is The Loewe additivity line (Eq. (5)). The isobole for zero interaction of a mutually nonexclusive model (Eq. (9)) is the same curve as that of the Bliss independence model with γ = 1.0.