FPTP ...) In STV 2nd preference won't harm 1st choice

[Bart Ingles]

Craig Carey wrote:
> 
> At 08:36 15.12.99 , Bart Ingles wrote:
> >Markus Schulze wrote:
> ...
> >> Example:
> >>
> >>   7 voters vote A > B > C.
> >>   6 voters vote B > A > C.
> >>   8 voters vote C > B > A.
> >>
> ...
> 
> >The claim under AV/IRV that your second choice will never harm your
> >first choice is also false -- the six BAC voters can attempt to coerce
> >some of the ABC voters into supporting B, either by truncating or by
> >order reversal (announcing their plans publicly before the election.
> 
> If that is the STV method, then the second choice can't harm the
>  candidate of the first preference. The word "false", could be changed
>  to the word "true".

Single-winner STV.

If the middle group truncates, there is a chance that some of the first
group will rank B first, in order to prevent C from winning.  If the
second group instead votes BAC, the first group has no reason to support
B, and so A wins instead of B.  Therefore the middle group's second
choice harms the candidate of their first preference (B).