Transcript 2.1 Weighted Voting Systems

§ 2.1 Weighted Voting Systems
Weighted Voting
 So far we have discussed voting
methods in which every individual’s vote
is considered equal--these methods
were based on the concept of “one
voter--one vote.”
 Weighted voting, is based on the idea
of “one voter--x votes”--in other words,
some voters ‘count more’ than others.
Weighted Voting Systems
 More rigorously stated, any formal
voting system arrangement in which the
voters are not necessarily equal in
terms of the number of votes they
control is called a weighted voting
system.
 For the sake of simplicity we shall only
examine motions--votes involving only
two choices/candidates.
Weighted Voting Systems
 Weighted voting systems are
comprised of:
1. Players - The groups, or individuals
that can cast votes.
2. Weights of the players - The number
of votes each player controls.
3. Quota - The smallest number of votes
needed to pass a motion.
Weighted Voting Systems
 Notation:
We will use N to refer to the number of
players in our system.
The players will be denoted P1 , P2 , P3 ,
. . . , PN .
Their corresponding weights are w1 , w2
, w3 , . . . , wN .
The letter q will be used to represent the
quota.
Weighted Voting Systems
 Using this notation we can represent
the entire weighted voting system as:
[ q : w1 , w2 , w 3 , . . . , wN ]
 Here the quota is listed first and the
weights are given in decreasing order.
Weighted Voting Systems
 The quota, q, must always be larger
than half the number of votes and not
more than the total number of votes.
Stated mathematically,
w 1 + w2 + w 3 + . . . + w N < q ≤ w 1 + w 2 +
w3 + . . . + w N
2
Example 1: Suppose that the board of
a small corporation has four shareholders,
P1 , P2 and P3 . P1 has 8 votes, P2 has 4
votes, P3 has 2 votes and P4 has 1. If at
least two-thirds of the votes are needed to
pass a motion then describe this system
using the ‘bracketed’ notation.
Example 2: Consider weighted voting
system with four players, P1 , P2 , P3 and
P4 . P1 has three times as many votes as
P2 . P2 has twice as many votes as P3
and P4 (which have the same number of
votes). If a simple majority is all that is
necessary to pass a motion then describe
this weighted voting system.
Weighted Voting Systems
 Notice in the last example that P1 could
pass or block any motion. In such a
situation, P1 would be called a dictator.
 In general, a player is a dictator if the
player’s weight is bigger than or equal
to the quota.
 Whenever there is a dictator, all of the
other players are irrelevant--such a
player with no power is called a dummy.
Weighted Voting Systems
 Now look back at example 1. You
might notice that no motion could pass
in that weighted system without the
support of P1 , but that P1 would still
need the support of at least one other
voter in order to pass a motion.
 Any player who is not a dictator, but
can block the passing of any motion has
what is referred to as veto-power.
Example 3: (Exercise #10 pg 73) In each
of the following weighted voting systems,
determine which players, if any, (i) are dictators;
(ii) have veto power; (iii) are dummies.
(a) [ 27 : 12, 10, 4, 2 ]
(b) [ 22 : 10, 8, 7, 2, 1 ]
(c) [ 21 : 23, 10, 5, 2 ]
(d) [ 15 : 11, 5, 2, 1 ]
Example 4: The US Senate is currently
composed of 55 Republicans, 44 Democrats
and 1 Independent (who votes with the
Democrats). Suppose 6 Republican senators
decided to form their own “Consensus Party”
(yes, I know this is even sillier than voting
muppets). Further suppose that following such
defections each party keeps its members strictly
in line.
Example 4: The US Senate is currently
composed of 55 Republicans, 44 Democrats
and 1 Independent (who votes with the
Democrats). Suppose 6 Republican senators
decided to form their own “Consensus Party”
(yes, I know this is even sillier than voting
muppets). Further suppose that following such
defections each party keeps its members strictly
in line.
We might describe this weighted voting system
as:
[ 51 : 49, 45, 6 ]
Example 4: The US Senate is currently
composed of 55 Republicans, 44 Democrats
and 1 Independent (who votes with the
Democrats). Suppose 6 Republican senators
decided to form their own “Consensus Party”
(yes, I know this is even sillier than voting
muppets). Further suppose that following such
defections each party keeps its members strictly
in line.
We might describe this weighted voting system
as:
[ 51 : 49, 45, 6 ]
While it might seem that both the Democrats
and Republicans hold more power than the