[EM] Explaining PR-STV

[Kathy Dopp]

Ralph,

I think you've forgotten some crucially important points in your
explanation of how STV is counted. My comments below...

> From: Raph Frank <raphfrk at gmail.com>
> Subject: [EM] Explaining PR-STV

> PR-STV is based on 4 main principles
>
> 1) Each voter gets 1 vote and they can vote for any candidate they want.
>
> ** All votes are equal. **

To clarify, add..

"All votes are equal"... *if* they are counted but some voters' never
have their 2nd or 3rd choices counted at all or before their 2nd or
3rd choice candidates are eliminated.


>
> 2) The 5 candidates who get the most votes get a seat.

often *not true* but it is complex to explain how in STV a candidate
with more votes might be eliminated and a candidate with fewer votes
win instead due to nonmonotonicity which itself is due to the unequal
treatment of voters' votes whereby voters who support the least
popular candidates have the most say in which candidates are
eliminated, etc.

>
> I am assuming 5 seats are to be filled, but the system works for any number.
>
> 3) If you vote for a losing candidate, your vote is transferred to
> your next choice

This is only true in special circumstances in STV/IRV, namely your
vote for a losing candidate is *only transferred to your next choice
**if** either:

1. your vote for a losing candidate occurs in early rounds so that
your next choice has not yet been eliminated, and

2. your vote for a losing candidate is for a losing candidate who does
not lose in the final elimination round, in which case your later
choices will never be considered.

(in other words, it is more accurate to say that in STV if your vote
for a losing candidate is for one of the least popular losing
candidates who is eliminated early on, then your vote will be
transferred to your next choice.)

>
> This reason for this rule is is so that you can safely give your first
> choice to your favourite even if he is a weak candidate.

This is a wholly, entirely, deceptively false statement. In IRV/STV
your first choice vote can always hurt the chances of your 2nd choice
candidate winning.

>
> If he doesn't win, your vote will be transferred to your next highest
> choice, until it gets to a candidate who can win a seat.
>
> ** Voting for a weak candidate doesn't mean you are "throwing your
> vote away". **

Yes. this would be more accurately rephrased "Be careful to vote for a
very very weak candidate first if you do not want your later more
popular candidates to lose."


>
> 4) If you vote for a candidate who gets more votes than he needs, the
> surplus is transferred to your next choice.

Again, this is only true in special situations similar to those
mentioned above for having your vote for a losing candidate
transferred.


>
> The Quota is simply the minimum number of votes a candidate needs in
> order to be guaranteed to be one of the top 5.
>
> If 5 candidates had a quota of votes, then even if all the rest of the
> votes go to one of the other candidate, he would have less than the
> quota.

You forget to mention that often STV can not fill all the seats unless
the quota is reduced to account for all the voters whose ballot
choices have been expired or eliminated so that many many voters in
STV are prohibited from participating in the final counting rounds.

Hence any jurisdiction which has adopted STV have had to eliminate any
requirement for majority winners, etc. since the method most often
fails to find sufficient candidates that meet the quota.

>
> If you vote for a candidate and he gets twice the Quota, then he only
> needs half of your vote to get elected.
>
> He keeps half of your vote and the rest of your vote would go to your
> next choice.
>
> ** Voting for a strong candidate also doesn't mean you are "throwing
> your vote away". **

totally false statement depending on the definition of "strong". There
are many examples where voters in STV are only allowed to have a vote
counted for one candidate even though they are supposed to be electing
a multi-seat *at-large* council, or where the *strong* candidate makes
it to the final counting round and then loses, where a *strong*
candidate (the first choice of *all* voters in a pairwise comparison)
is eliminated in an early round and a less *strong* candidate wins,
etc. etc.

I don't have time to finish rebutting this plethora of misinformation,
but no one should be fooled by it.

Cheers,
-- 

Kathy Dopp

Town of Colonie, NY 12304
phone 518-952-4030
cell 518-505-0220

http://utahcountvotes.org
http://electionmathematics.org
http://kathydopp.com/serendipity/

Realities Mar Instant Runoff Voting - 18 Flaws and 4 Benefits
http://electionmathematics.org/ucvAnalysis/US/RCV-IRV/InstantRunoffVotingFlaws.pdf

Voters Have Reason to Worry
http://utahcountvotes.org/UT/UtahCountVotes-ThadHall-Response.pdf

Checking election outcome accuracy --- Post-election audit sampling
http://electionmathematics.org/em-audits/US/PEAuditSamplingMethods.pdf