[EM] Proportional multi-winner ranked voting methods - guidelines?

[VoteFair]

On 2/23/2017 10:43 AM, James Gilmour wrote:
 > Please see the attached results of some STV-PR elections
 > to the Northern Ireland Assembly.
 >
 > If Canada had results like those from its Federal and
 > Provincial elections no-one would be calling for
 > electoral reform in Canada.

The referenced data supports my belief that the number of seats per 
district is heavily correlated with the number of popular political parties.

In this case there are 6 seats per district, and there are about 6 
popular political parties.  Specifically the political-party count 
includes 4 popular parties that apparently fill the first 4 seats, and 
then another 4 mid-popular parties that compete for the next 2 seats (in 
each district).  (The least-popular parties rarely get seats.)

Although in this case the correlation -- between seats per district and 
number of popular political parties -- is a simple correlation, other 
correlations are possible.

As a hypothetical example, if there were 5 seats per district, two 
dominant political parties might typically win the first four seats (two 
seats per party), and less-popular parties might often win the remaining 
5-th seat (with different parties winning in different districts).

The more political parties there are, the messier it is to create a 
ruling coalition that really represents what the voters want.  Too often 
a coalition compromises on issues that are most important to the voters 
in those parties.  If anyone doesn't understand this disadvantage of 
needing coalitions, which I've explained before, please ask.

One of the advantages of VoteFair ranking is that it favors fewer 
political parties in order to let the voters form their own coalitions 
-- in the form of very popular political parties.  Yet the method allows 
as many parties as the voters really want.

VoteFair ranking accommodates as many parties as possible, yet limits 
the number of candidates in each race.  Here is how:

* In every election the popularity of parties is re-measured, and the 
popularity rankings are used in the next election.

* Each of the two most popular parties can offer two candidates (per party).

* The mid-popular parties can offer just one candidate each.

* The currently least-popular parties are not allowed to offer any 
candidates in the race -- in that district, based on party popularities 
within that district.  (The popularity of parties can vary from district 
to district, and only that district's popularity rankings are used for 
these cutoffs.)

* The limited number of candidates allows voters to get to know these 
candidates better, which is important for ranking them meaningfully 
(without saying "after my first and second choice I have an equal 
dislike for the remaining candidates").

In a sense, VoteFair ranking does the opposite of what closed-list PR 
does.  Closed-list PR gives control to party leaders, instead of giving 
control to the voters.  In contrast, VoteFair ranking gives control to 
the voters, so that "insider" candidates (who are liked by party 
leaders) cannot get elected -- to either the district seats or the 
nationwide seats -- unless they are ALSO the most popular candidates 
according to the voters.

The latest development in the U.S. Democratic party serves as an example 
of the unfairness of a party being controlled by insiders, rather than 
voters.  Specifically the new chairperson of the Democratic party was 
the insider favorite.  Most Democratic voters would have preferred the 
candidate who was favored by Bernie Sanders and Elizabeth Warren, who 
the voters prefer as the most popular Senators in the Democratic party.

Since the above PR-related comments are about closed-list PR, I'll add 
that open-list PR is better, yet it uses single-mark ballots, which are 
vulnerable to tactics that take advantage of vote splitting.

Another important point about STV is that it fails to consider all the 
preferences of all the voters.  Instead, like IRV, it is based on the 
mistaken belief that the candidate with the most currently-first-choice 
"votes" is most popular, and the candidate with the fewest 
currently-first-choice "votes" is least popular.  This flaw makes it 
easier for the "wrong" (less-popular) candidate to win a seat.

This flaw was recently demonstrated in the U.S. Republican presidential 
primary election, where single-mark ballots were used and there were 
more than a dozen (12) candidates.  The more candidates there are in a 
race (not counting the ones who get very few votes), the more dramatic 
this unfairness can be.

Expressed another way, the first priority should be to fill seats with 
the most popular candidates, and the second priority should be to get 
some degree of proportional results for the remaining seats.

VoteFair ranking follows this prioritization.  Specifically:

* 1-2-3 ballots and pairwise counting are used to fill the first seat in 
each district.

* The second seat in each district is filled by the most popular 
candidate (using 1-2-3 ballots and pairwise counting) after 
proportionally reducing the influence of the voters who are already 
well-represented by the first-seat winner.

* Some remaining "nationwide" seats are allocated to political parties 
based on the voters' party preferences (i.e. voters rank political 
parties and the first choice is used for this purpose).  The nationwide 
seats are filled with candidates who were the most popular (in their 
party) within their district (but failed to win a district seat), and 
who got the most support when compared across district boundaries.

This approach is much fairer than allowing parties to choose their 
favorite insiders.

In particular, it defeats the strategy of each party offering just one 
"insider" candidate.  (The second candidate from the same popular party 
is optional, but a popular party that does not offer a second candidate 
will become less popular because the manipulation becomes obvious.)

To repeat my original key point, any voting method that only looks at 
one voter's currently-top candidate at a time cannot produce fair 
results.  Fair results can only be assured if all the preferences of all 
the voters are considered pairwise (not simplistically one-at-a-time).

Just hiding the unfairness -- by making adjustments according to 
political-party "quotas" -- is not solving the underlying unfairness.

Yes, proportionality is desireable, but not at the expense of ending up 
with less-popular candidates.

Both can be achieved, but:

* PR sacrifices fairness by not providing a fair way to control which 
candidates win each party's seats.

* STV sacrifices fairness in several ways:

** Through its counting method.

** Through what I'll call "round-off errors" if it is used to fill more 
than 2 seats per district (and if the number of seats does not happen to 
match the current number of popular political parties).

** It does not handle adjustments in "nationwide" seats, after the 
round-off errors have accumulated over all the districts.

Questions?  Please ask.

Richard Fobes


On 2/23/2017 10:43 AM, James Gilmour wrote:
>> Richard Fobes (VoteFair)  Sent: 23 February 2017 17:54
>> However, as I stated before, STV would not provide fair results if it were used for a full national legislature.
>>
>> Recently, in Canada, some people have been promoting the idea of using STV to elect about 5 MPs (members of parliament) from
>> each district (which they call a "riding").  That would produce very unfair results!
>> That's what I had in mind when I referred to using STV repeatedly.
>
> Please see the attached results of some STV-PR elections to the Northern Ireland Assembly.
>
> If Canada had results like those from its Federal and Provincial elections no-one would be calling for electoral reform in Canada.
>
> James Gilmour
> Edinburgh, Scotland