Seats-to-votes ratio

The seats-to-votes ratio, also known as the advantage ratio, is a measure of equal <a href="/facts/Political_representation/EfU0v8bj">representation of voters</a>. The equation for seats-to-votes ratio for a political party i is:

a
 
 i
 
 
 
 =
 
 s
 
 i
 
 
 
 /
 
 
 v
 
 i
 
 
 
 
 {\displaystyle \mathrm {a_{i}} =s_{i}/v_{i}}
 
,
where 
 
 
 
 
 
 v
 
 i
 
 
 
 
 
 {\displaystyle \mathrm {v_{i}} }
 
 is fraction of votes cast for that party and 
 
 
 
 
 s
 
 i
 
 
 
 
 {\displaystyle s_{i}}
 
 is fraction of seats won by that party.
In the case both seats and votes are represented as fractions or percentages, then every voter has equal representation if the seats-to-votes ratio is 1. The principle of equal representation is expressed in slogan <a href="/facts/One_man%2c_one_vote/dY1BVlMS">one man, one vote</a> and relates to <a href="/facts/Proportional_representation/69pRhsx9">proportional representation</a>. The seats-to-votes ratio is used as the basis for the <a href="/facts/Gallagher_index/gzJ61XQQ">Gallagher index</a> method of analyzing proportionality or disproportionality.
Related is the votes-per-seat-won, which is inverse to the seats-to-votes ratio.
Also related are the principles of <a href="/facts/Political_representation/EfU0v8bj">one man one vote and representation by population</a>.

Seats-to-votes ratio open-in-new

Seats-to-votes ratio