• wethepeopleofhk

American 'Ranked Choice Voting' versus 'Modified Borda Count' MBC

Updated: Feb 23


Please see our related MBC blogs:



WTPOHK put this question to Peter Emerson of deborda.org and debordavote.org :

We note the Americans like to talk about 'Ranked Choice Voting' but we want to be sure how best to present MBC before we say or do anything.


Peter's answer:

So let me first comment on the “Ranked Choice Voting” which is otherwise known as the “Alternative Vote AV,” (which is used in Australian elections) or the “Single Transferable Vote STV,” (which, in multi-member seats is PR-STV, which is what we have in our elections in Ireland) or, when used in decision-making, it is also called “Instant Run-off Voting IRV,” in North America and “Preference Voting PV,” in Australasia.


I’ll call it AV. It can be unfair, and capricious.


Consider the following profile in which, obviously the winner should be C.




In a plurality vote, A wins.


In a two-round system, nothing has a majority, so it’s a second round between A and B, which (if everyone’s preferences stay the same), B wins on 65 to A’s 35.

With AV, C is eliminated and its 32 votes go to B, so again, B wins on 65 to A’s 35.


With an MBC, the scores are:

A 105 + 0 + 65 = 170

B 99 + 64 + 35 = 198

C 96 + 136 + 0 = 232


So C is the winner, as it should be. It would also win a Condorcet count: C 2, B 1, A 0.


So, yes, AV can be unfair.


And you’d get similar outcomes, if the profile was like this.



But now consider the situation when the C voters are torn between A and B.




In this situation, under AV, the stage (ii) score line is A 51, B 49; so A wins. But if just two of those C voters give their 2nd preference not to A but to B, so that’s 18 to B and 14 to A, then the stage (ii) score line is B 51, A 49; so now B wins. So A’s and B’s 2nd preferences count for nothing, and just two of C’s 2nd preferences can completely swing the outcome.


Yes. AV can be capricious.


That said, AV is better than plurality voting (or first-past-the-post).


With an MBC, the scores are:

A 105 + 0 + 65 = 170

B 99 + 64 + 35 = 198

C 96 + 136 + 0 = 232


So C is the winner, as it should be.


It would also win a Condorcet count: C 2, B 1, A 0.


So, yes, AV can be unfair.





[Updated 23 February 2021] America looking at multi-option preferencial voting!