LEGISLATIVE EFFECTS OF SINGLE-MEMBER VS MULTIMEMBER DISTRICTS

Theory: This project uses mathematical logic and results from spatial models to explain how parties in a legislature elected under a multi-m ember district system will differ from those elected under single-memb er plurality, holding all else constant. Hypothesis: Under most circum stances, parties elected under multi-member districts will be more ide ologically diverse than those elected under single-member plurality, a ll else being equal. Methods: The above hypothesis is tested using int erest group ratings for members of the Illinois General Assembly, a le gislative body that has used both single-member and multi-member syste ms to elect its members. Results: During the time when the Illinois Ho use was elected by multi-member districts and the Senate was elected b y single-member districts, parties in the House were consistently more ideologically diverse than their counterparts in the Senate. This dif ference disappears after the House adopts a single-member district sys tem.