The Banzhaf index in representative systems with multiple political parties

The proposed modification of the Banzhaf index is used to evaluate voter po wer in representative multiple-party (i.e., more than two) systems. The mod ified index shows that a voter's ability to affect the outcome of legislati ve decisions increases asymptotically as the inverse of the square root of the district's population. The square-root effect thus holds even in cases involving more than two parties. (C) 1999 Academic Press.