IRV and Breadth of Support
Proponents of Instant Runoff Voting (including its limited form, called “Ranked Choice Voting” or “RCV” for short) often claim that IRV elects candidates with both depth and breadth of support. For example:
“RCV elects candidates that elicit both passionate and broad support, both of which are necessary qualities in a leader.” ~California RCV proponent
The following five-candidate RCV election is won by candidate Z. (Note that on first sight it may seem peculiar to see such a few number of voters, but you get equivalent results by multiplying by 1,000. This format is just for ease of understanding.)
# of voters their ranking
But note that candidate C has twice as many first-place rankings as Z (4 versus 2), and is preferred to Z by a 71% majority (12 of the 17 voters). C has greater depth and breadth than Z, but RCV still elects Z. And A is preferred to Z by an 88% majority (15 of the 17 voters).
Appealing to a Broad Middle
Another way to consider breadth of support is a candidate who is moderate. This candidate virtually by definition appeals to the largest breadth of the electorate. But IRV is poor at electing this candidate as well. For more, see our article on the "center squeeze" effect.