From Plurality Rule to Proportional Representation

I consider the decision of a parliament that might change the electoral system for the forthcoming elections from plurality rule to proportional representation. Parties are o¢ ce-motivated. They care about winning and about the share of seats obtained. I consider two di¤erent scenarios of how parties in the government share the spoils of o¢ ce: Equally or proportionally to their share of seats. If the government is formed by a single party and parties expect that each party will obtain the same share of votes in the next election the electoral rule will never be changed. That is, for a change to occur the government should be formed by a coalition. I ?nd that a change is more likely to occur when the number of parties is larger and also when the spoils of o¢ ce are shared equally among the members in the governing coalition. I extend these results to analyze the decision of a change from a less proportional rule to a more proportional one.