 
Summary: Notes for Session 7, Basic Voting Theory, Summer School 2011 T.Seidenfeld 1
Notes for Session 7 Basic Voting Theory
We follow up the "Impossibility" (Session 6) of pooling expert probabilities, while
preserving unanimities in both unconditional and conditional probabilities. Here
we explore the power of group voting as a substitute for group pooling.
Assume that the group decision problem involves mmany, pairwise exclusive social
acts, e.g., the options might be candidates in an election, or (exclusive) bills before a
legislature. And there are nmany citizens, or voters, or legislators in our group.
Each voterj (j = 1, ..., n) has an ORDINAL ranking of the moptions, as summarized
in the table below. The quantities r·j are the ranks assigned by voterj to the m
many acts. We'll let a rank of 1 be best, and a rank of m be worst.
Ties are allowed by sharing the average rank for those tied in the ranking.
For example, if two acts tie for best position they share rank 1.5 ( = (1+2) / 2), etc.
Thus, for each voter, the sum of the ranks equals m(m+1)/2.
Notes for Session 7, Basic Voting Theory, Summer School 2011 T.Seidenfeld 2
TABLE of nmany Voters' Rank Order of mmany acts
Act1
Act2
Acti
Actm
