top of page
Tom Monto

Kevin Baas tried to improve on STV

in guest post on opavotes website Kevin Baas tried to improve on STV


However when he conducted a demonstation election using STV to show its flaws, he used a lower quota than even Droop. He used seats divided by seats plus 1, while Droop is (seats /seats plus1) plus1.


This did in fact make a difference because the model election used just 36 votes spread over four candidates. so for example a surplus was 3 (12-9), not 2 (12-10)


but his idea that eliminated candidates should retain the non-transferable vots that they have at time of elimination is work-able. But as non-transferable votes are seldom as much as quota, it is not likely to make much difference in real-life election.


His mathematical proof that Hare is the appropriate quota, not Droop at all, is intriquing. Catherine Helen Spence for many years said the same but I believe her support for Hare was based on just on how much easier Hare was to explain than Droop.

However as his mathematical proof shoong how normal STV is flawed is based on seats/seats plus 1, not Droop his argument loses some of its persuasiveness.

Oddly he says "The +1 in the denominator skews the seats-votes curve in favor of whichever party has the majority, resulting in representation that is not proportional."

I assume when he says "not proportional," he means more than it deserves proportionately.

This statement is surprising as usually it is phrased that Hare is hard on larger parties, and that Droop (which uses the +1 in the denominator) is more fair to large parties,

and it is not said that Droop disproportionately favours large parties.


he says "You should only eliminate a ballot permanently when it's used to meet quota." this seems at first confusing when ballots are not eliminated in STV. only candidates are eliminated.

But he means ballots should not be put out of the contest unless used to compose quota of a succ. candidate. They should not be put off to side as non-transferable vote or exhausted vote when a candidate is eliminated.

And then if that temporarily-eliminated candidate gets enough vote transfers, he may be able to pass the least-popular candidate and get back in the running.

A slight chance exists that could happen but mostly such a new rule means the same candidate will be eliminated again and again by being re-energized but then immediately eliminated again when he is again at the bottom of the list.

there-energized candidate cannot be just ignored if he bears usable votes as that might skew results for the other candidates.

Such a new rule would save a party from trying to ensure that enough of its candidates survive to the end to grab up seats, while another less-careful party with more disparate vote tallies among its candidates suffers loss of its cand. at the bottom of the list and then is denied receiving its due share of seats due to insufficient number of surviving candidates. so in that way it might be useful.


in addition to using Hare as Quota and candidates only being temporarilly eliminated, Baas suggest another new rule:

Re-calculate the quota just before testing for it, instead of just once at the beginning. This compensates for ballots that have run out of choices. (the non-transferable votes)


that is before each count, re-calculate quota based on votes still in play.


This seems actually to be odd as we have determined that votes formerly taken out as non-transferable are now back in as being owned by the cand. that was only temporarily eliminated previously.


His 4th new rule is about pairing off the candidates which I don't fully understand


===========

The 4 major changes from traditional STV are:

  • Uses the correct quota of votes/seats (don’t swallow the spider) 

  • Only permanently eliminate ballots if they are used to make quota (don’t swallow the fly) 

  • Recalculate quota right before checking (‘cause ballots could have run out of choices) 

  • Temporarily eliminate sets of candidates in order of fewest "rank demotions" to most, ordering all possible combinations. 

He then states:

I have 3 major changes from the traditional way of counting ranked choice votes:

  1. Restore ballots that haven’t been used to meet a quota. (as opposed to not restoring) 

  2. Use votes/seats as the quota. (commonly known as “Hare quota”). (as opposed to using an unbalanced quota of votes/(seats+1)) [and he means to do this for each stage or count] [as mentioned, actually STV uses Droop, not votes/seats plus 1.

  3. Temporarily ignore combinations of candidates based on the number of choice demotions it results in. (sorted from least to most) (as opposed to fewest votes) 


He says that adopting only one of them by itself gives little or no improvement over normal STV. and not doing even one of them means little or no improvement even if other two are done..


As you might gather from above, I weakly support

  • replacing Hare with Droop (although maybe not for reason Bass is saying) Anyways transfers have little or no effect on the ranking of candidates in the first count so are not worthy of much attention to my mind.)

  • re-energizing candidates who have a large store of non-transferable votes - although I am not looking forward to the extra counts needed.

But I don't see need to reset quota if the votes used as base to calculate quota are reduced by non-transferable votes (which under his rules might come back into use anyway)

or are  votes used as base to calculate quota reduced by the number of votes set aside with the successful candidates as well?

does it go from 1000 votes/ 4 seats to 750 votes/3 seats, for example?

actually that make no difference, anyway.


And if we did derive a lower quota for later counts, is that wise? For fairness sake, do we want later winners to win with lower quota than earlier winners? I am not sure we do.


And I totally don't get the paired-candidate thing.


If we look at the vote-count method Baas proposes, we see quite a lot of complication

so I don't recommend it but I reprint it here if anyone else is interested.


Baas's proposed oligorithm for STV Vote count

The method 


STEP 0: Make a copy of the ballots - these will be referred to as the "original" copy, even though they'll be altered (reweighted) due to surplus vote transfers.


Determining the next winner:


STEP 1: Determine quota 1: Count how many ballots are left (using the weighted value of the ballot), divide by number of seats left to fill. This is the quota.


STEP 2: order all combinations of candidates

  1. Compute all combinations of candidates (e.g. {a},{b},{c},{a,b},{b,c},{a,c},{a,b,c}) 

  2. For each such combination, count how many "choice demotions" would happen if those candidates are removed, in order for every voter to have a 1st choice candidate, or run out of choices. For instance, if a person's choices are {a,b,c,d}, and a,b & d are removed, then the result is {c}, and it counts as 2 demotions. (Since what is now the 1st choice used to be the 3rd). Remember to use the weighted value of the ballot in counting demotions. 

  3. Sort all combinations by how many choice demotions they produce, least to most. 

  4. Ties are broken by fewest ballots affected. 

  5. Ties on that, in turn, are broken by most candidates eliminated this way. 

  6.  Add the "empty set" (no candidates) to the beginning.

STEP 3 (loop): Make a local copy, and try removing the next combination. (first time through, this is removing no combinations)

  1.  Make a local copy of the ballots. For the remainder we will be operating on this local copy. 

  2.  Take the next set of candidates in the sorted demotion list (if this is the first time, this will be an empty set). 

  3.  Remove those candidates from the ballot, and promote all the choices so it doesn't skip any ranks. if a ballot is out of choices, disregard it. 

STEP 4: Check for quota (repeat from step 3 if not reached)

  1. Check if any candidate has reached or exceeded quota (using their weighted value -- always use the weighted value). 

  2.  If one has, the one with the most votes is elected. 

  3.  If none have reached quota, revert to the local copy you made in step 3, and repeat, using the next candidate combination in the sorted list. 

STEP 5: Winner selected, transfer surplus votes proportionally (on original copy).

  1. The candidate with the most first place votes is elected. 

  2. Re-weight the ballots that were used to make quota - that have that person listed as first in the local copy. Their new weight is whatever their previous weight was, times 1-(quota/(the sum of their current weights)). This re-weighting applies to the original ballots, not our local copy. 

  3. Remove the elected candidate from all ballots, and shift the ranks up to make them sequential. If any ballot runs out of choices, remove it. 

STEP 6: Repeat as necessary. Repeat from the step 1 for the next seat.

=======================



3 views

Recent Posts

See All

Comments


bottom of page