There is a long-standing and easily-disproved criticism of STV.
It is usually expressed this way:
all other things remaining equal (for otherwise it has no ground to stand on at all) if a candidate receives more votes, he or she may do worse than if he or she did not have those additional votes.
BUT all other things cannot remain equal.
if a candidate receives more votes, either the total number of vote must increase or some other candidate must get less votes.
If the total number of votes increases, then there is no way a candidate will do worse with the additional votes than without them - except through the exceptional, intricate and artificially-arranged order of eliminations leading sometimes to the wanted skewed result.
But if Candidate A gets more votes and other changes happen, Candidate A may do worse.
If votes are transferred from Candidate C to Candidate A and these two specific candidates share little support, it is possible that Candidate A will do worse if Candidate C through this change drops to being least-popular candidate. In that case, when it is time to eliminate a candidate from the bottom. Candidate C will be eliminated, and likely his or her votes will be transferred in greater number to Candidate B than to A, putting Candidate B ahead of A. if that boost is enough it will push Candidate B, not A, over the quota threshold to be elected, PERHAPS filling the last open seat before Candidate A collects enough votes to do so.
On the other hand, If votes are transferred from Candidate C to Candidate A and these two specific candidates share much support, it is likely that Candidate A will do better because Candidate C will drop lower in the rankings and be that much earlier eliminated, and that much earlier his or her votes will be transferred to Candidate A to finally put Candidate A over Quota.
(But in historical practice in the Canadian experience of STV, almost always there were no un-elected un-eliminated candidates at the end. In all cases in Alberta, eliminations were continued until the remaining candidates were declared elected just by being the last ones on their feet. The order of elimination did not make any difference because all but the winner were eliminated.) The point is that mostly the anti-STV argument rests on the statement that the only change is a candidate gets more votes but does worse. BUT other changes must take place. The anti-STV argument obviously would be weaker if it went like this: if a candidate gets more votes under STV and other changes happen to the vote tallies, the candidate will do worse. But that is actually how the argument goes. And it is how STV works - in different situations a candidate may do worse or may do better. And what I am talking about is how somewhat lower-ranking candidates may or may not be elected depending on circumstances - that is, those who come in third or fourth or fifth or sixth in the first count of a STV election. BUT to use the anti-STV argument to apply to a First-count first-place candidate - well I don't see it. To say that a candidate in first place will not be elected but would have been if it was in second place eludes imagination -- for one thing, there has been no STV election where the two front leaders in the first count were not elected - unless the number of seats is very small, barely proportional, just two or three seats. But there is no way - no way - that in a STV district with five or more open seats the two front leaders in the first count are not elected, maybe they will not be first elected - although almost always they will be - but they always eventually take a seat in the end. I bet my boots on it.
Thanks for reading.
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