Sainte-Laguë method

The Sainte-Laguë method (French pronunciation: ​[sɛ̃.tə.la.ɡy]), also known as the Webster method or Schepers method, is a highest quotient method for allocating seats in party-list proportional representation used in many voting systems. It is named in Europe after the French mathematician André Sainte-Laguë and in United States after statesman and senator Daniel Webster. The method is quite similar to the D'Hondt method, but uses different divisors. In most cases the largest remainder method delivers almost identical results. The D'Hondt method gives similar results too, but favors larger parties compared to the Sainte-Laguë method. Often there is an electoral threshold, that is a minimum percentage of votes required to be allocated seats.

Before Sainte-Laguë introduced the method, based on Webster's proposal from 1832, in 1842 the method was adopted for proportional allocation of seats in United States congressional apportionment (Act of June 25, 1842, ch 46, 5 Stat. 491) It was then replaced by Hamilton method and in 1911 the Webster method was reintroduced.

The Sainte-Laguë method is used in Bosnia and Herzegovina, Iraq, Kosovo, Latvia, New Zealand, Norway and Sweden. In Germany it is used on the federal level for the Bundestag, and on the state level for the legislatures of Baden-Württemberg, Bremen, Hamburg, North Rhine-Westphalia, Rhineland-Palatinate, and Schleswig-Holstein).

The Sainte-Laguë method was used in Bolivia in 1993, in Poland in 2001, and in the elections to the Palestinian Legislative Council in 2006. A variant of this method, the modified Sainte-Laguë method, was used to allocate the proportional representation (PR) seats in the Constituent Assembly poll of Nepal in 2008.

The method has been proposed by the Green Party in Ireland as a reform for use in Dáil Éireann elections, and by the United Kingdom Conservative-Liberal Democrat coalition government in 2011 as the method for calculating the distribution of seats in elections to the country's upper house of parliament.

Description of the method

After all the votes have been tallied, successive quotients are calculated for each party. The formula for the quotient is

$\text{quot} = \frac{V}{2s+1}$

where:

• V is the total number of votes that party received, and
• s is the number of seats that party has been allocated so far, initially 0 for all parties.

Whichever party has the highest quotient gets the next seat allocated, and their quotient is recalculated given their new seat total. The process is repeated until all seats have been allocated.

The Sainte-Laguë method does not ensure that a party receiving more than half the votes will win at least half the seats; nor does its modified form. For example, with seven seats available and the votes split 53,000, 24,000 and 23,000, the allocation would be three, two and two seats respectively.

denominator	/1	/3	/5	/7	/9	/11	/13	Seats won (*)	True proportion
Party A	53,000*	17,666*	10,600*	7,571	5,888	4,818	4,076	3	3.71
Party B	24,000*	8,000*	4,800	3,428	2,666	2,181	1,846	2	1.68
Party C	23,000*	7,666*	4,600	3,285	2,555	2,090	1,769	2	1.61

The d'Hondt method differs by the formula to calculate the quotients $\left( \text{quot} = \frac{V}{s+1}\right)$.

Webster, Sainte-Laguë, and Schepers

Webster proposed the method in United States Congress in 1832 for proportional allocation of seats in United States congressional apportionment. In 1842 the method was adopted (Act of June 25, 1842, ch 46, 5 Stat. 491). It was then replaced by Hamilton method and in 1911 the Webster method was reintroduced.

According to some observers the method should be treated as two methods with the same result, because Webster method is used for allocating seats based on states' population and Saint Lague based on parties' votes. Webster invented his method for legislative apportionment (allocating legislative seats to regions based on their share of the population) rather than elections (allocating legislative seats to parties based on their share of the votes) but this makes no difference to the calculations in the method.

Webster's method is defined in terms of a Droop quota as in the largest remainder method; in this method, the quota is called a "divisor". For a given value of the divisor, the population count for each region is divided by this divisor and then rounded to give the number of legislators to allocate to that region. In order to make the total number of legislators come out equal to the target number, the divisor is adjusted to make the sum of allocated seats after being rounded give the required total.

One way to determine the correct value of the divisor would be to start with a very large divisor, so that no seats are allocated after rounding. Then the divisor may be successively decreased until one seat, two seats, three seats and finally the total number of seats are allocated. The number of allocated seats for a given region increases from s to s + 1 exactly when the divisor equals the population of the region divided by s + 1/2, so at each step the next region to get a seat will be the one with the largest value of this quotient. That means that this successive adjustment method for implementing Webster's method allocates seats in the same order to the same regions as the Sainte-Laguë method would allocate them.

The German physician Hans Schepers, at the time Head of the Data Processing Group of the German Bundestag, in 1980 suggested that the distribution of seats according to d’Hondt be modified to avoid putting smaller parties at a disadvantage. German media started using the term Schepers Method and later German literature usually calls it Sainte-Laguë/Schepers.

Modified Sainte-Laguë method

Some countries, e.g. Nepal, Norway and Sweden, change the quotient formula for parties that have not yet been allocated any seats (s = 0) from V to V/1.4. That is, the modified method changes the sequence of divisors used in this method from (1, 3, 5, 7, ...) to (1.4, 3, 5, 7, ...). This gives slightly greater preference to the larger parties over parties that would earn, by a small margin, a single seat if the unmodified Sainte-Laguë's method were used. With the modified method, such small parties do not get any seat; these seats are instead given to a larger party.

Norway further amends this system by utilizing a two-tier proportionality. The number of members to be returned from each of Norway's 19 constituencies (counties) depends on the population and area of the county: each inhabitant counts one point, while each square kilometer counts 1.8 points. Furthermore, one seat from each constituency is allocated according to the national distribution of votes.

Threshold for seats

Often a threshold or barrage is set, and any list party which does not receive at least a specified percentage of list votes will not be allocated any seats, even if it received enough votes to have otherwise receive a seat. Examples of countries using the Sainte-Laguë method with a threshold are Germany and New Zealand (5 %), although the threshold does not apply if a party wins at least one electorate seat in New Zealand or three electorate seats in Germany. Sweden uses a modified Sainte-Laguë method with a 4 % threshold, and a 12 % threshold in individual constituencies (i.e. a political party can gain representation with a minuscule representation on the national stage, if its vote share in at least one constituency exceeded 12%). Norway has a threshold of 4 % to qualify for the seats from each constituency that is allocated according to the national distribution of votes. This means that even though a party is below the threshold of 4% nationally, they can still get seats from constituencies they are particularly popular in.

See also

• Hagenbach-Bischoff quota

External links

• Seats Calculator with the Sainte-Laguë method
• Java implementation of Webster's method at cut-the-knot
• Elections New Zealand explanation of Sainte-Laguë
• Java D'Hondt, Saint-Lague and Hare-Niemeyer calculator