Majority bonus system

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The majority bonus system (MBS), sometimes referred to as the reinforced proportionality electoral system is a semi-proportional method of election multiple representatives. The majority bonus is typically classified a mixed electoral system, as it integrates both the proportionality and winner-take-all principles to provide mixed-member majoritarian representation. An academic term for such a hybrid system is fusion^[1], which means an independent combination of two systems in which the two formulas are mixed within the same district (the district in question may be a single, nationwide constituency). This makes it distinct from other mixed systems such as parallel voting (superposition) and coexistence. A majority bonus may also be one of the properties of a supermixed system.

The goal of the majority bonus system is to give extra seats in a legislature to some parties (most commonly the largest party), with the aim of providing government stability, particularly in parliamentary systems. The size of the majority bonus can vary significantly and usually it is a fixed number of seats, but it may be conditional on the number of votes received by parties. A relatively small majority bonus (such as in the reinforced proportionality system of Greece) may not always guarantee that a single party can form a government. A the same time, as the majority bonus is allocated in a non-compensatory manner, therefore if the majority bonus if as high as 50% and the largest party which has 50% of the popular vote receives it, this party may win as many as 75% of all seats. This differentiated it from the similar majority jackpot system.

It is currently used in Greece,^[a] French Polynesia and on a local level in Italy and France ^{[citation needed]}. In Argentina, it is used in the Chamber of Deputies of Santa Fe, Chubut, and Entre Ríos.^{[citation needed]}

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