Coalitions and Probability

Abstract

Looking at the process of coalition formation in the parliament one can find the following two ways of analysis:

• — political party’s aspiration to have simple majority,

• — a proximity between members of joined parties in an ideological space.

The assumption of parties’ proximity is very reasonable when a power distribution is analysed. The paper contains definition of coalition, as a formation that has the largest probability in an ideological space. The taxonomy method was used as a basic method for computing probability for any coalition. Thus, one can modify classic way of computing Shapley-Shubik index. An example of polish parliament was computed.