The starting point is simple. If a constituency includes four seats, a proportion of the votes in the order of 25% is necessary to win one of them. On the other hand, if there are 100 seats, subject to any national minimum 1% of the vote is sufficient to win one seat. Constituency size is therefore critical. The situation can be summarised by the following formula which calculates a representativeness limit: L is the number of votes necessary to be certain of winning a seat.

       total number of votes
L = _____________________ + ε (the smallest possible value)
         number of seats + 1

Take the example of a four-member constituency: L = 100%/4+1 + ε