The main advantage of IRV is that it isn't a particularly strategic vote. You put the candidates you in the order of your actual preference, and that's it (ther

The main advantage of IRV is that it isn't a particularly strategic vote. You put the candidates you in the order of your actual preference, and that's it (there are edge cases, but compared with other systems, pretty rare ones, and their complexity tends to actually discourage strategic behaviours like elevating a decent candidate you think is more likely to win than your first choices). The strategic considerations you actually might want to make are very basic (if you really, really want to make sure someone doesn't win, you can rank parties you're pretty unimpressed with ahead of them). A ratings ballot, on the other hand, involves massive amounts of thinking. First of all, the concept of what might represent an "honest" approach to intensity of preferences is open to debate. It's US culture to give their Uber driver max marks and tip the serving staff 20%; is this an honest reflection of the intensity of the average American's enthusiasm for service workers relative to people from non-American cultures or simply what they've been taught to do? And real world electoral situations give you all kinds of incentives to do other things (like give your preferred candidate max marks and all the other candidates 0, or all the candidates you don't hate at least 9 out of 10). Is the person who bullet votes max marks for his preferred candidate because that's what the campaign literature suggested really worth more votes than the person who carefully evaluated all the candidates on their merits but doesn't think any of the candidates are worth more than 6 out of 10? With approval voting it's arguably even worse because there's a massive dilemma over whether to vote positively for the candidate(s) you want or negatively to eliminate the risk of candidates you want to lose. Obviously this applies unevenly to different demographics: put someone downright nasty towards a particular demographic on the ballot paper, and suddenly that demographic is under pressure to Approve every other candidate, whilst others continue to happily only vote for candidates they actually want. If you design an efficiency metric with the arguably unjustifiable assumption that votes always represent either a perfect expression of the intensity of their preferences or a simple uniform strategic vote, and you assume that the proportion of people voting strategically is unaffected by voting system, it is unsurprising that voting systems whose main shortcomings are strategic complexity perform well. Even looking at that data, IRV actually outperforms nearly all the systems if you assume IRV voters are honest and voters using the other system are very strategic which isn't unreasonable given the incentive structures of the different systems.