The arithmetic of the Bundestag elections

On 27 September 2009, when Germany goes to the polls for the Bundestag elections, everyone will have two votes to cast. The first vote is used to elect a constituency candidate, in other words, the politician who should be sent to Parliament to represent the voter's region. The second vote determines the relative strengths of the parties in the Bundestag.

The constituency candidate who receives the most first votes is elected - regardless of how his or her party performs overall. These constituency seats ensure that every region in Germany is represented in the Bundestag.

The second vote is decisive

The second cross made on the ballot paper, the 'second vote', is used to determine the relative strengths of the parties in the Bundestag. This is therefore the decisive vote, because it dictates which parliamentary group or coalition of parties will later have a majority allowing them to elect their preferred candidate as Federal Chancellor.

If a party fails to meet the requirement that it receive more than five per cent of all votes cast nationwide (also known as the 'five per cent clause'), it is not represented in the Bundestag - unless the party has won at least three constituency seats, in which case it is taken into account in the distribution of seats to the parties' lists in the individual Länder (federal states).

Proportional representation with elements of first-past-the-post

The German electoral system is based on proportional representation, but contains some added elements of first-past-the-post. Who holds the majority in the Bundestag is, however, initially determined by the number of second votes won by the individual parties. In the past, the distribution of seats was calculated using what is known as the Hare/Niemeyer method, which reflects the strength of the smaller parties more accurately than some other techniques.

However, for the Bundestag elections in September, the Sainte-Laguë/Schepers method will be used for the first time. The decision to apply this method was taken by the Bundestag on 17 March 2008, to avoid possible paradoxes caused by the previous method. The number of seats to which a party is entitled is calculated according to its share of the second votes. Seats are allocated first to the candidates who won the most first votes in the constituencies, before the remaining seats are allocated to the candidates on the party list in the Land concerned, in the order in which they are listed.

Distribution of parliamentary seats

Half of the total of 598 Members of the Bundestag are politicians who won the most first votes in one of Germany's 299 constituencies. The other half of the Members are elected via party lists in the individual Länder. These lists are drawn up by the parties before the election. They nominate candidates they consider to be particularly well-qualified to serve in Parliament - or who are believed to be popular with the electorate.

The places at the top of the list are generally considered to be 'safe', with election likely. A certain degree of risk remains, however: if the number of constituency seats won by a party is as high as the number of seats it is entitled to according to its share of the second votes, then even the top candidate on the list will not be elected - unless he or she has won a constituency seat.

Overhang mandates and relative strengths of the parties

The number of constituency seats won is extremely significant, because it can affect the composition of Parliament, which is otherwise fixed according to the share of second votes won. If a party wins more constituency seats than it is entitled to according to its share of the second votes, it nonetheless keeps these additional seats, known as 'overhang mandates'.

The Bundestag currently has 612 Members. The reason for this is that there were 16 such overhang mandates at the last Bundestag elections four years ago, resulting in the Bundestag having a total of 614 Members. Following a ruling by the Federal Constitutional Court, two seats which became vacant (one Member died, another resigned) were not filled, as the party concerned (the CDU) had overhang mandates in the Länder concerned.

In July 2008 the Federal Constitutional Court ruled that an effect known as 'negative vote weight', which can arise in connection with overhang mandates, is unconstitutional. This effect refers to the possibility that winning more second votes can nonetheless cause a party to lose a seat, and vice versa. The Court has given Parliament until 2011 to change the system.