The Interpretation of the Laakso-Taagepera Effective Number of Parties

In this paper, we present a general statistical framework within which we can draw a new interpretation of the Laakso-Taagepera effective number of parties fragmentation index. With the particular method of sampling with probability proportional to the party sizes, we show that the Laakso-Taagepera effective number of parties is the inverse of the size biased version of the traditional expected party size in shares. Further, we provide an axiomatic definition of the Laakso-Taagepera effective number of parties.Fragmentation, effective number of parties, concentration index, size biased sampling, length biased sampling.

A note on the monotonicity and superadditivity of TU cooperative games

In this note we make a comparison between the class of monotonic TU cooperative games and the class of superadditive TU cooperative games. We first provide the equivalence between a weakening of the class of su- peradditive TU games and zero-monotonic TU games. Then, we show that zero-monotonic TU games and monotonic TU games are different classes. Finally, we show under which restrictions the classes of superadditive and monotonic TU games can be related.TU cooperative games; superadditivity; monotonicity

The effective number of relevant parties : how voting power improves Laakso-Taagepera’s index

This paper proposes a new method to evaluate the number of rel- evant parties in an assembly. The most widespread indicator of frag- mentation used in comparative politics is the ‘Effective Number of Par- ties’(ENP), designed by Laakso and Taagepera (1979). Taking both the number of parties and their relative weights into account, the ENP is arguably a good parsimonious operationalization of the number of ‘relevant’ parties. This index however produces misleading results in single-party ma jority situations as it still indicates that more than one party is relevant in terms of government formation. We propose to modify the ENP formula by replacing proportions of seats by voting power measures. This improved index behaves more in line with Sar- tori’s definition of relevance, without requiring additional information in its construction.Voting power indices; Effective Number of Parties; Party system fragmentation; Relevance; Coalition Formation

On the measurement of Fragmentation

In this paper we propose a new party-system fragmentation measure as equivalent number of parties that fully takes into account the pivotal power of parties. The novel approach we adopt in the method of construction for an index of fragmentation allows us to take advantage of the theory of generalized means. We first construct the (class of) quasi-arithmetic mean(s) with Banzhaf power weight function for the party sizes and then, given the average size, we derive an equivalent-number of parties

A note on the monotonicity and superadditivity of TU cooperative games

In this note we make a comparison between the class of monotonic TU cooperative games and the class of superadditive TU cooperative games. We first provide the equivalence between a weakening of the class of su- peradditive TU games and zero-monotonic TU games. Then, we show that zero-monotonic TU games and monotonic TU games are different classes. Finally, we show under which restrictions the classes of superadditive and monotonic TU games can be related

On the measurement of Fragmentation

In this paper we propose a new party-system fragmentation measure as equivalent number of parties that fully takes into account the pivotal power of parties. The novel approach we adopt in the method of construction for an index of fragmentation allows us to take advantage of the theory of generalized means. We first construct the (class of) quasi-arithmetic mean(s) with Banzhaf power weight function for the party sizes and then, given the average size, we derive an equivalent-number of parties.Fragmentation, Effective number of parties, Voting power, Effective average size, Generalized means

Contractually stable networks

We develop a theoretical framework that allows us to study which bilateral links and coalition structures are going to emerge at equilibrium. We define the notion of coalitional network to represent a network and a coalition structure, where the network specifies the nature of the relationship each individual has with his coalition members and with individuals outside his coalition. To predict the coalitional networks that are going to emerge at equilibrium we propose the concept of contractual stability which requires that any change made to the coalitional network needs the consent of both the deviating players and their original coalition partners. We show that there always exists a contractually stable coalitional network under the simple majority decision rule and the component-wise egalitarian or majoritarian allocation rules. Moreover, requiring the consent of group members may help to reconcile stability and efficiency.networks, coalition structures, contractual stability, allocation rules.

Contractually stable networks

We develop a theoretical framework that allows us to study which bilateral links and coalition structures are going to emerge at equilibrium. We define the notion of coalitional network to represent a network and a coalition structure, where the network speciÖes the nature of the relationship each individual has with his coalition members and with individuals outside his coalition. To predict the coalitional networks that are going to emerge at equilibrium we propose the concept of contractual stability which requires that any change made to the coalitional network needs the consent of both the deviating players and their original coalition partners. We show that there always exists a contractually stable coalitional network under the simple majority decision rule and the component-wise egalitarian or majoritarian allocation rules. Moreover, requiring the consent of group members may help to reconcile stability and e¢ ciency.Networks ; Coalition Structures ; Contractual Stability ; Allocation Rules Networks ; Strong efficiency

Contractually Stable Networks

We develop a theoretical framework that allows us to study which bilateral links and coalition structures are going to emerge at equilibrium. We define the notion of coalitional network to represent a network and a coalition structure, where the network specifies the nature of the relationship each individual has with his coalition members and with individuals outside his coalition. To predict the coalitional networks that are going to emerge at equilibrium we propose the concept of contractual stability which requires that any change made to the coalitional network needs the consent of both the deviating players and their original coalition partners. We show that there always exists a contractually stable coalitional network under the simple majority decision rule and the component-wise egalitarian or majoritarian allocation rules. Moreover, requiring the consent of group members may help to reconcile stability and efficiency.Networks, Coalition Structures, Contractual Stability, Allocation Rules

Contractually stable networks

We develop a theoretical framework that allows us to study which bilateral links and coalition structures are going to emerge at equilibrium. We define the notion of coalitional network to represent a network and a coalition structure, whre the network specifies the natyure of the relationship each individual has with his coalition members and with individuals outside his coalition. To predict the coalitional networks that are going to emerge at equiibrium we propose the concept of contractual stability which requires that any change made to the coalitional network needs the consent of both the deviating players and their original coalition partners. We show that there always exists a contractually stable coalitional network under the simple majority decision rule and the component-wise egalitarian or majoritarian allocation rules. Moreover, requiring the consent of group members may help to reconcile stability and efficiencyNetworks; coaliation structures; contractual stability; allocation rules