Distributed Multi-Voting: Difference between revisions

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[[File:DMV procedure.jpg|thumb|DMV procedure]]
Each voter has 100 points to distribute among the candidates according to his preferences. All candidates in the vote have 0 points by default.
# For each single vote, get the normalized votes on all subsets conteiningcontaining at least 2 candidates. Add up the points for each candidate of the normalized votes, obtaining the converted original vote.
# After obtaining all the converted original votes, the candidate with the lowest sum, of the converted votes, loses.
# Eliminate the loser from all the original votes, and setting the candidate with the lowest score in each vote to 0. Repeat the whole process from the beginning, leaving as many winner as you like.
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* set the candidate (s) with the lowest score between A,B,C to 0.
* apply the following formula on the other candidates:
S = sum of the points of the candidates in the subset.
v0 = value of candidate X, before normalization
v1 = value of candidate X, after normalization.
<math>\begin{equation}
v1=\frac{v0}{S} \cdot 100
\end{equation}</math>
 
In normalization for the % of victory, use the same formula without setting the candidate with the lowest score to 0.
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If the candidates of the subset, in a certain vote, all have the same score different from 0 then, before normalization, don’t set the lowest score to 0.
 
==Tactical vote resistance==
==Criteria==
 
The original vote of the voter through point 1 of the procedure is converted, and the vote obtained is in part of the type:
{| class="wikitable" style="text-align:center"
<!-- criteria headers -->
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0;"
! rowspan=1 |
! rowspan=1 style="border-left: 2px solid #a0a0a0;" | [[Majority criterion|Majority]]
! rowspan=1 | [[Majority loser criterion|Maj. loser]]
! rowspan=1 | [[Mutual majority criterion|Mutual maj.]]
! rowspan=1 | [[Condorcet criterion|Condorcet]]
! rowspan=1 | [[Condorcet loser criterion|Cond. loser]]
! rowspan=1 | [[Smith criterion|Smith]]
! rowspan=1 | [[Independence of irrelevant alternatives|IIA]]
! rowspan=1 | [[w:Independence of clones criterion|Clone proof]]
! rowspan=1 style="border-left:2px solid #a0a0a0;" | [[Monotonicity criterion|Monotone]]
! rowspan=1 | [[Consistency criterion|Consistency]]
! rowspan=1 | [[Participation criterion|Participation]]
! rowspan=1 style="border-left:2px solid #a0a0a0;" | [[Later-no-help criterion|Later-no<br>Help]]
! rowspan=1 | [[Later-no-harm criterion|Later-no<br>Harm]]
! rowspan=1 | [[Favorite betrayal criterion|Favorite<br>betrayal]]
|- style="font-size:80%;"
 
* ranking (Borda), because the points tend to be distributed linearly in the converted vote (see all cases).
<!-- Methods -->
|-
! [[Distributed_Multi-Voting|DMV]]
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
! style="background: #ffc7c7; font-weight: inherit;" | No*
|}
 
* range (Score), because by distributing the points in quite different quantities, the candidates tend to keep their score in the converted vote (see A,B,C in cases [1], [2], [3], [5] ).
{| class="wikitable" style="text-align:center; float: right; margin: 0px 20px 5px 20px;"
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0;"
! rowspan=1 style="border: none; background: white;" |
! A
! B
! C
! D
|-
 
* cumulative, because the points distributed in the converted votes are however limited and fixed (700 in the case [1], 1000 in the cases [2] and [4], 1100 in the cases [3], [5], [6] based the number of candidates evaluated).
|- style="font-size:80%; font-weight: inherit; background: white;"
! style="text-align:right;" | [1] original vote
| style="font-weight: bold;" | 100
| 0
| 0
| 0
|-
 
Meets [[Honesty criterion]] under the same assumptions as the [[Distributed Voting#Tactical vote resistance|Distributed Voting]].
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0; font-weight: inherit; background: white;"
! style="text-align:right;" | converted vote
| 700
| 0
| 0
| 0
|-
 
Under the same assumptions as the [[Distributed Voting#Tactical vote resistance|DV]], this system also tries to satisfy the [[Honesty criterion|Perfect Honesty criterion]], by applying a conversion of the vote which serves to drastically reduce the deviation from the honest one.
|- style="font-size:80%; font-weight: inherit; background: white;"
! style="text-align:right;" | [2] original vote
| style="font-weight: bold;" | 99
| style="font-weight: bold;" | 1
| 0
| 0
|-
 
Example
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0; font-weight: inherit; background: white;"
Candidates: [A B C D E]
! style="text-align:right;" | converted vote
Honest vote: [50 30 15 5 0]
| 697
Tactical vote: [90 6 3 1 0]
| 303
Honest converted vote: [1118 820 486 176 0]
| 0
Tactical coverted vote: [1434 622 390 153 0]
| 0
Error in %: [22% 24% 20% 13% 0] Avg error = 20%
|-
633 out of 2600 is around 25%.
 
On average about 80% of the score, expressed in the tactical vote, is honest at the start of the counting, even if the voter used a tactical vote. A good representation of interests is also provided.
|- style="font-size:80%; font-weight: inherit; background: white;"
! style="text-align:right;" | [3] original vote
| style="font-weight: bold;" | 96
| style="font-weight: bold;" | 4
| style="font-weight: bold;" | 1
| 0
|-
 
'''Other properties'''
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0; font-weight: inherit; background: white;"
! style="text-align:right;" | converted vote
| 686
| 292
| 122
| 0
|-
 
In cases [1] and [2] it’s noted that the addition of 1 point on B, left the score of A practically unchanged in the converted vote, but in case [2] it obtained 303 points for B (same speech observing the case [3] or even [5] ); this means that the voter has an interest in expressing his preference towards B. At the same time, the voter doesn’t even have the interest of giving his limited points to candidates he doesn’t really support (reduced [[Vote splitting]]) .
|- style="font-size:80%; font-weight: inherit; background: white;"
! style="text-align:right;" | [4] original vote
| style="font-weight: bold;" | 51
| style="font-weight: bold;" | 49
| 0
| 0
|-
 
==Systems variants (Multi-Voting method)==
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0; font-weight: inherit; background: white;"
! style="text-align:right;" | converted vote
| 553
| 447
| 0
| 0
|-
 
In general, starting from a vote, all the votes are obtained for each subset of the candidates (some normalization is used), and then they are added together obtaining the converted vote. Subsequently, the count on the converted votes is applied.
|- style="font-size:80%; font-weight: inherit; background: white;"
! style="text-align:right;" | [5] original vote
| style="font-weight: bold;" | 75
| style="font-weight: bold;" | 20
| style="font-weight: bold;" | 5
| 0
|-
 
===Score Multi-Voting (SMV)===
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0; font-weight: inherit; background: white;"
! style="text-align:right;" | converted vote
| 627
| 342
| 131
| 0
|-
 
The following formula is used to normalize the votes:
|- style="font-size:80%; font-weight: inherit; background: white;"
! style="text-align:right;" | [6] original vote
| style="font-weight: bold;" | 35
| style="font-weight: bold;" | 33
| style="font-weight: bold;" | 32
| 0
|-
 
[MIN, MAX] = ''[0,9]'' = range of the voting system.
|- style="font-size:80%; border-bottom: 2px solid #a0a0a0; font-weight: inherit; background: white;"
[min, max] = ''[3,6]'' = lower and higher value among the candidates of the subset, in a vote.
! style="text-align:right;" | converted vote
Cnew = new value of the candidate, in a vote.
| 490
C = old value of the candidate, in a vote.
| 381
| 229
| 0
|-
|}
 
<math>\begin{equation}
No* = the DMV can fail all the criteria but the cases in which they fail are extremely rare (less frequent than many others voting systems that don't meet the same criteria).
C_{new} \ =\ MIN\ +\ ( C\ -\ min) \cdot \frac{MAX\ -\ MIN}{max\ -\ min}
\end{equation}</math>
 
If max = min, then Cnew = MAX
The original vote of the voter through point 1 of the procedure is converted, and the vote obtained is in part of the type:
 
* ranking (Borda), because the points tend to be distributed linearly in the converted vote (see all cases).
 
* range (Score), because by distributing the points in quite different quantities, the candidates tend to keep their score in the converted vote (see A,B,C in cases [1], [2], [3], [5] ).
 
* cumulative, because the points distributed in the converted votes are however limited and fixed (700 in the case [1], 1000 in the cases [2] and [4], 1100 in the cases [3], [5], [6] based the number of candidates evaluated).
 
Example of normalized voting for a subset of candidates:
The DMV in any case meets the [[Independence of Worst Alternatives|IWA]].
 
Original vote: A[9] B[6] C[5] D[3] F[0] G[1] H[1]
===Resistance to strategic votes===
Subset {A,C,F}: A[9] C[5] F[0]
Subset {A,B,C}: A[9] B[2.25] C[0]
Subset {C,D,F}: C[9] D[5.4] F[0]
Subset {B,C,D}: B[9] C[6] D[0]
Subset {B,C,D,F}: B[9] C[7.5] D[4.5] F[0]
Subset {G,H}: G[9] H[9]
Subset...
 
By adding the converted votes, the candidate with the highest sum wins.
The DMV is extremely resistant to tactical votes, that ignore the election results.
 
===STAR Multi-Voting (STAR-MV)===
The way in which the converted vote is obtained means that the voter doesn’t have a great interest in accumulating their points all on the same candidate. In cases [1] and [2] it’s noted that the addition of 1 point on B, left the score of A practically unchanged in the converted vote, but in case [2] it obtained 303 points for B (same speech observing the case [3] or even [5] ); this means that the voter has an interest in expressing his preference towards B. At the same time, the voter doesn’t even have the interest of giving his limited points to candidates he doesn’t really support (reduced dispersion of points) .
The DMV can be subject to tactical votes in which candidates change the order of their preferences based on the results of the elections; to use these tactical votes you must:
 
The converted votes are calculated, as in the Score Multi-Voting, on which the STAR count is then applied.
* are sufficiently aware of the expected results of an election (hard).
* fully understand the functioning of the DMV.
* be willing to take risks, because these tactical votes can backfire on the voter if they fail.
 
[[Category:Cardinal voting methods]]
Overall in practical contexts it’s very difficult to create an effective strategic vote in the DMV.
[[Category:Single-winner voting methods]]
[[Category:Multi-winner voting methods]]
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