On Tue, 14 Jul 2009, Simon Lyall wrote:
Following a discussion in the Internetnz list I've made a little post on tactical voting that some may find interesting:
http://blog.darkmere.gen.nz/2009/07/hacking-internetnz-council-vote/
Disclaimer: I'm noting a serious expert on voting systems so there might be an error with my suggestions.
Simon's suggestion is based on the understanding that voters whose first preference has been elected do no participate in any more voting rounds (all their other preferences are ignored). This appears to be borne out by the 2008 election for councillors: the first to be elected was Jamie, who had 16 first preferences. After his election, 16 fewer voters participated in the subsequent rounds. The description of the voting system at http://www.internetnz.net.nz/about/rules/2006-07-21-voting-rules is missing some vital information. It states, at step 1: "All 1st preference votes are counted for each candidate". Nowhere does it mention anything about redistributing lower-ranked preferences, only that lowest-ranked candidates are "temporarily" removed from consideration. The literal reading would lead one to conclude that there is no point voting for any candidate other than your first preference, and that most certainly is *not* what preferential voting is supposed to be about. So one is left to infer that indeed preferences *are* taken into account, despite the literal wording, but there is nothing to suppose that this works any differently when candidates are removed on steps 3 and 4. So I conclude that the methodology as implemented is not what is written in the rule. And furthermore, it's broken, because (a) it reintroduces "tactical voting", the lack of necessity for which is supposed to be one of the great strengths of Preferential Voting; and (b) it under-represents persons who vote for "popular" candidates (especially during the first round). I hasten to point out that the converse approach -- of leaving all voters "in" for all rounds is actually worse in terms of fairness, because it unfairly favours bloc-voting (a marginal majority can direct the election of ALL the positions). But at least with such a scheme a voter wouldn't need foreknowledge of the result in order to cast an optimal vote. A more reasonable middle-ground system would be the (considerably simpler) approach of eliminating lowest-polling candidates until there remains only sufficient candidates to fill the available positions, and then declare them all to be elected. (Such a system is "reasonably fair" provided that the ratio of candidates-to-positions is smaller than the ratio of voters-to-candidates, but does still slightly bias against supporters of popular candidates.) An alternative "fairer" middle-ground system is to eliminate successful candidates in the current manner, but (a) set the electability threshold T as Vt/N (where Vt is total of votes for all candidates and N is number of positions still to be filled); and (b) don't completely discount a successful candidate's supports' votes in subsequent rounds (as currently), but rather reduce them by a factor that yields fair treatment of supporters of popular candidates. I've done up an explanation at http://www.sig.net.nz/~martin/internetnz-voting along with an example of how this would have applied to last year's council election. -Martin