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Question
consider the weighted voting system 8: 7, 4, 1
find the shapley - shubik power distribution of this weighted voting system.
list the power for each player as a fraction:
$p_1$:
$p_2$:
$p_3$:
Step1: Calculate total number of permutations
The number of players is \(n = 3\). The total number of permutations of \(n\) players is \(n!=3!=3\times2\times 1=6\).
Step2: Define the players and quota
Let \(P_1\) have weight \(w_1 = 7\), \(P_2\) have weight \(w_2 = 4\), and \(P_3\) have weight \(w_3 = 1\). The quota \(q = 8\).
Step3: Analyze each permutation for pivotal - player
- Permutation \((P_1,P_2,P_3)\): The cumulative weights are \(7\) (after \(P_1\)), \(7 + 4=11\) (after \(P_2\)). \(P_2\) is the pivotal - player.
- Permutation \((P_1,P_3,P_2)\): The cumulative weights are \(7\) (after \(P_1\)), \(7+1 = 8\) (after \(P_3\)). \(P_3\) is the pivotal - player.
- Permutation \((P_2,P_1,P_3)\): The cumulative weights are \(4\) (after \(P_2\)), \(4 + 7=11\) (after \(P_1\)). \(P_1\) is the pivotal - player.
- Permutation \((P_2,P_3,P_1)\): The cumulative weights are \(4\) (after \(P_2\)), \(4 + 1=5\) (after \(P_3\)), \(5+7 = 12\) (after \(P_1\)). \(P_1\) is the pivotal - player.
- Permutation \((P_3,P_1,P_2)\): The cumulative weights are \(1\) (after \(P_3\)), \(1 + 7=8\) (after \(P_1\)). \(P_1\) is the pivotal - player.
- Permutation \((P_3,P_2,P_1)\): The cumulative weights are \(1\) (after \(P_3\)), \(1 + 4=5\) (after \(P_2\)), \(5+7 = 12\) (after \(P_1\)). \(P_1\) is the pivotal - player.
Step4: Calculate Shapley - Shubik power
The Shapley - Shubik power of a player is the fraction of permutations in which the player is the pivotal - player.
The number of times \(P_1\) is the pivotal - player is \(4\). So, the Shapley - Shubik power of \(P_1\) is \(\frac{4}{6}=\frac{2}{3}\).
The number of times \(P_2\) is the pivotal - player is \(1\). So, the Shapley - Shubik power of \(P_2\) is \(\frac{1}{6}\).
The number of times \(P_3\) is the pivotal - player is \(1\). So, the Shapley - Shubik power of \(P_3\) is \(\frac{1}{6}\).
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\(P_1:\frac{2}{3}\)
\(P_2:\frac{1}{6}\)
\(P_3:\frac{1}{6}\)