General Luce model

We extend the Luce model of discrete choice theory to satisfactorily handle zero-probability choices. The Luce mode struggles to explain choices that are not made. The model requires that if an alternative y is never chosen when x is available, then there is no set of alternatives from which y is chosen with positive probability. In our model, if an alternative y is never chosen when x is available, then we infer that y is dominated by x. While dominated by x, y may still be chosen with positive probability, when grouped with a comparable set of alternatives.