An equation for the single operant is called the quantitative law of effect. The equation relates absolute response and reinforcement rates, using alternative sources of reinforcement as the context. The equation may be derived from a restatement of the proportional matching law and is written as B,,I(B,, + Bd = R,,I(R,, + Rd . In this equation, Be refers to all behaviour directed to extraneous sources of reinforcement, and R, represents these sources.