Two Fair Coin Flips Suffice to Beat Distortion Three in Metric Voting

We show that two fair coin flips suffice to improve on the optimal deterministic distortion of three in ordinal metric voting. Given any complete ranking profile, one can fix four equiprobable candidate slots, allowing repeats, whose expected social cost is at most 2.97029814 times that of any original candidate under every compatible metric. We prove existence by coupling an activated source lottery with a nonlinear envelope for the empirical distribution of four draws. An exact signed expectation bound makes the same list valid across metrics. Rational certificates verify the threshold inequalities on their full continuous domain and the four-draw expectation.

Authors

Publication Details

Journal
Zenodo (CERN European Organization for Nuclear Research)
Published
2026-11-10
DOI
https://doi.org/10.5281/zenodo.24090606
Primary Topic
Game Theory and Voting Systems
Type
preprint
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preprint

Two Fair Coin Flips Suffice to Beat Distortion Three in Metric Voting

Fangge Cui
Zenodo (CERN European Organization for Nuclear Research)
Game Theory and Voting Systems
preprint

Two Fair Coin Flips Suffice to Beat Distortion Three in Metric Voting

Fangge Cui
preprint en

Abstract

We show that two fair coin flips suffice to improve on the optimal deterministic distortion of three in ordinal metric voting. Given any complete ranking profile, one can fix four equiprobable candidate slots, allowing repeats, whose expected social cost is at most 2.97029814 times that of any original candidate under every compatible metric. We prove existence by coupling an activated source lottery with a nonlinear envelope for the empirical distribution of four draws. An exact signed expectation bound makes the same list valid across metrics. Rational certificates verify the threshold inequalities on their full continuous domain and the four-draw expectation.

Zenodo (CERN European Organization for Nuclear Research)
Game Theory and Voting Systems
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