[EM] Tactical voting under a jury model

Colin Champion colin.champion at routemaster.app
Sun Mar 6 05:41:36 PST 2022

I wrote in another thread that "under a jury model with tactical voting, 
I have some evidence that the best methods are the ones with the worst 
reputations: FPTP and IRV and their extensions". Perhaps some people 
would like to see the evidence. The following table gives mean valence 
losses (so smaller is better) under a jury model with voters attempting 
a burial strategy. It has to be viewed in a fixed-width font.

            random   fptp    sptp     av   sinkhorn borda     mj coombs
           115.6767  4.2340 15.4462  3.4934 22.3533 21.3425    - 36.3451
          condorcet benham   btr    nanson minimax minisum    rp river  
schulze   asm
              -     3.5469  4.6945  9.5228  7.7089  8.0696  8.4014 
8.3864  9.6397  9.8513
condorcet+ random   fptp    sptp     av    borda
            9.9406  4.9425 11.5035  3.5441 14.2516
  copeland+ random  fptpf   fptpr    sptp    avf     avr    bordaf 
bordar minimaxfminimaxr
           11.4423  9.6349 10.7388 12.4150  9.5974 10.5371 14.4200 
12.7967  8.7613 12.0312
     smith+ random  fptpf   fptpr    sptp    avf     avr    bordaf 
bordar minimaxfminimaxrtideman   q&dc
            9.6397  4.9559  4.9856 11.5026  3.5442  3.5532 14.2516 
10.0643  7.7106  7.7106  4.0854  7.3363

AV (=IRV) seems to be best, while most Condorcet methods do badly and 
the Borda count does appallingly.

These results are from my own evaluation software; full details are at 
https://www.masterlyinactivity.com/condorcet/condorcet.html  The call is 
"condorcet 5 101 100000 jury:2+bur". Obviously the correctness of my 
code is not guaranteed.

I've never seen an evaluation under a jury model, even assuming sincere 
voting. I certainly don't rate such models highly, but I think 
discussions of voting need a model and spatial models aren't the whole 
truth, so it helps to keep alternatives in mind.


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