Voting Systems

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Popular voting systems

1. Plurality voting

(also called "First Past the Post")

every casts one vote for one option

whichever vote has most votes wins

problem since, suppose 5 options, and three get 20%, one gets 19%, and one gets 21%. That 21% wins. 

problem 2 (called spoiler effect): if two big parties, one with slight majority, and then one third, small party, then small party could 'steal' votes from big party, leading to the smaller of the two big parties to win, despite perhaps many small party voting preferring the bigger of the two big parties to begin with. 



2. Instant Runoff Voting

(also called Alternative voting)



everyone ranks all options

then we eliminate least popular, and take put those votes into those voter's second choice

rinse and repeat until only one is left (or when one has majority vote, i.e. >50%, since that just ends it)

could have same spoiler effect problem (for three party example) if one party is roughly taking a middle stance, and thus taking voters from both sides. Called 'center-squeeze' phenomenon. In this case, the actually honest more popular party, is squeezed out due to runoff elimination. 



3. Multiple round voting (basically above, except you can change your preference per round)

so suppose 'multiple' here is defined as two round

then first round, we find top 2 choices, then everyone votes on the top two again. 

however, since you can change your choice per round, this could potentially allow some gaming of the system,

like intentionally voting for a non-preferred choice just to take out a choice first. 


is the system Georgia and Louisianna uses for voting for their 2 senator seats (they call it runoff-elections)



4. Condorcet voting


essentially pit every 2 options against each other. so, all combinations of N choose 2. 

then whichever option wins the most matches is the winner, so plurality in that sense. 

but, has the problem where, it is possible to have a three way tie. Then you're can't select a winner. 



5. Approval voting 

(is a special case of range/score voting where each candidate can be scored from a range, the range here is 0-1) 

you can 'approve' of multiple parties at the same time, with equal weighting

then, the plurality wins. 

but due to 'chicken-dilemma', where voters strategically 'not approve' of their second or third choice in order to let their first choice win, a third, least approved party could actually win. 








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