Simple Optionally-Delegated Approval (simplified)
Simple Optionally-Delegated Approval (SODA) is a single-winner voting system based on approval voting, where voters can vote for as many candidates as they like. Unlike in approval, voters can choose to delegate their ballot to their favorite candidate, trusting the candidate to "complete the ballot" by deciding which other candidates to approve. The voters' ballots are counted and the totals are announced, and then candidates can choose to exercise the ballots delegated to them. At that point, candidates who do not expect to win can approve others whom they think would be good compromise options.
After all candidates exercise their delegated ballots, the winner is the candidate with the most approvals.
For simplicity, the ballot is organized like an approval ballot. It is assumed that voters who vote for only one candidate are intending to delegate their ballot to that candidate, unless they explicitly indicate otherwise using a "do not delegate" option. Thus, no voter's ballot is delegated without their consent.
Candidates are required to submit a rank-ordering of all the other candidates before the election. This serves two purposes. First, it helps voters understand how that candidate might choose to complete their delegated ballots. A voter who supports a candidate but disagrees with their rankings of others can complete their ballot themselves instead of delegating. Second, the prior rankings vastly decrease the opportunities for manipulation when the candidates exercise their ballots. When they exercise the ballots delegated to them, the candidates must approve others in a way that is consistent with the rank-ordering they submitted. In other words, they must take their submitted rank-ordering and choose a cutoff point, approving all candidates above that point and disapproving all candidates below that point. Thus, they cannot simply "sell their delegated votes" to the highest bidder.
To further decrease the opportunities for manipulation, candidates with the most approvals get the advantage of "moving first" in declaring how they will exercise their delegated ballots. This order is designed to encourage good outcomes in certain problematic situations. See the full Simple Optionally-Delegated Approval page for more information.