Plurality is inherantly flawed. California's recall of its governor will allow over a hundred candidates to run against each other, without a primary. If 50.1% of the voters oust the current governor, one of these candidates could become governor with less than 1% of the vote - so long as no other new candidate gets better than that, even though 49.9% of the voters would likely have preferred the recently recalled governor. This is insane. Plurality only works when there are one or two candidates. With three candidates, one could win with 34% of the votes, even if 66% of the voters would rather have either of the other two. We need a voting system that can reflect ranks to prevent that.
Instant Runoff Voting: This style is derived from runoff voting, a time-consuming method to ensure an electorate has the most support (or the least opposition). An election is held, and unpopular candidates are removed. Another election is then held with the remaining candidates and this process is repeated unti lthere is a sole winner. Instant Runoff does this all at once. Each voter ranks the candidates. The first choice is then used as the first vote. The candidate with the fewest votes gets eliminated, and is removed from the voter rankings. For many voters, this means they are now voting for another candidate. Repeat this process until there is a winner. Here is a Flash-animated example of instant runoff voting. More information can be found here, and the Massachusetts Citizens for Runoff Voting site is another good resource. ElectionMethods.org has a page of problems with Instant Runoff.
A simplification of this, Single Runoff, can be performed more quickly. Eliminate all but the top two candidates in a single run, then re-tally. Look, ma; no recursion!
Borda Count Voting: This is the point-based voting system; each voter ranks the candidates by using weighted votes. The first choice gets the most points and the last choice gets no points. More information is available at deborda.org and ElectionMethods.org.
Condorcet Voting: Compare each pair seperately (requires voters to rank the candidates in the same manner as the above two methods). More information on Condorcet voting can be found at ElectionMethods.org (which heavily favors it).
There are also other systems, such as Approval Voting, where you can vote for as many candidates as you wish (like an un-weighted Borda).
| [sample] | Borda | Runoff | Condorcet |
|
simple sample 6 ranked { A B C } 5 ranked { C B A } 4 ranked { B C A } A wins plurality with 40% |
A=12 B=19 C=14 B wins |
Single Runoff top 2 are A & C, (C→9) A=6, C=9 C wins Instant Runoff B eliminated, (C→9) A=6, C=9 C wins |
A v B: 6 v 9 A v C: 6 v 9 B v C: 10 v 5 A=0, B=2, C=1 B wins |
|
complex sample 18 ranked { A B C D E } 12 ranked { E C B D A } 10 ranked { D E C B A } 9 ranked { B D C E A } 4 ranked { C E B D A } 2 ranked { C D B E A } A wins plurality with 32.7% |
A=72 B=136 C=134 D=107 E=101 B wins |
Single Runoff top 2 are A & E, (E→37) A=18, E=37 E wins Instant Runoff cut C (E→16, D→12) cut B (D→21) cut E (D→37) cut A (D→55) D wins |
A v (B/C/D/E): 18 v 37 B v C: 27 v 28 B v D: 41 v 14 B v E: 29 v 26 C v D: 36 v 19 C v E: 33 v 22 D v E: 39 v 16 A=0, B=3, C=4, D=1, E=2 C wins |
In the above simple example, nine of fifteen people would rather B or C than A. In plurality, A wins with 40% of the votes. In Borda, B has the most over-all support. Instant Runoff eliminates B because too few pople were strongly in favor of B. The four votes for B then count towards C and C has nine votes to A's six, so C wins.
In plurality, if a voter wants the under-dog (B in this example) but has a strong preference of one of the other candidates over the remaining, this voter is forced to vote for this "more realistic" choice, such as voting for C instead of B just to avoid a victory for A. This was dubbed the "Nader Factor" in the 2000 presidential election, after Ralph Nader, the Green Candidate.
ElectionMethods.org put together a pretty informative page on a base set of specifications for acceptable voting methods. It seems weighted against Instant Runoff (which meets none of the criteria, while plurality meets two of nine) and in favor of Condorcet voting (which meets eight of nine).
Other good resources include The Constitution Society's page on Voting Theory and Reform, a PBS TeacherSource resource on Elections and Voting, the dmoz Voting Systems directory, and ElectionMethods.org.