APA Dictionary of Psychology

in behavioral studies, a formula in the form of a power function (y = ax^b ) that describes the choice between two alternatives in terms of the ratio (y) of rates of occurrence of (or time spent in) each alternative and the ratio (x) of the rates of reinforcement of the two alternatives. The exponent (b) of the function indexes sensitivity to reinforcement rates, and the coefficient (a) indexes inherent bias for one of the alternatives. When both a and b are equal to 1.0, the formula makes the same prediction as the matching law.