The D'Hondt method, also called the Jefferson method or the
greatest divisors method, is a method for allocating seats in parliaments among
federal states, or in party-list proportional representation systems. It
belongs to the class of highest-averages methods.
The method was first described in 1792 by future U.S. president Thomas Jefferson. It was re-invented independently in 1878 by Belgian mathematician Victor D'Hondt[1], which is the reason for its two different names.
Proportional representation systems aim to allocate seats to parties approximately in proportion to the number of votes received. For example, if a party wins one-third of the votes then it should gain about one-third of the seats. In general, exact proportionality is not possible because these divisions produce fractional numbers of seats. As a result, several methods, of which the D'Hondt method is one, have been devised which ensure that the parties' seat allocations, which are of whole numbers, are as proportional as possible. Although all of these methods approximate proportionality, they do so by minimizing different kinds of disproportionality. The D'Hondt method minimizes the number of votes that need to be left aside so that the remaining votes are represented exactly proportionally. Only the D'Hondt method (and methods equivalent to it) minimizes this disproportionality. Empirical studies based on other, more popular concepts of disproportionality show that the D'Hondt method is one of the least proportional among the proportional representation methods. The D'Hondt slightly favours large parties and coalitions over scattered small parties. In comparison, the Sainte-Laguë method, a different divisor method, reduces the reward to large parties, and it generally has benefited middle-size parties at the expense of both large and small parties.
[1] Victor Joseph Auguste D'Hondt (b. Ghent, Belgium 20 November 1841 – d. Ghent, Belgium 30 May 1901) was a Belgian lawyer and jurist of civil law at Ghent University. From 1885 he served as professor of civil and fiscal law at the University of Ghent. In 1896 he was awarded the title Officer in the Belgian Order of Leopold.