A further variable affecting the make-up of electoral systems is the number of rounds of voting. Most ballots consist of one or two rounds but there are also systems with n rounds.

a. Single-round ballots: these can be used not only in proportional representation systems but also in first-past-the-post systems. This type of ballot generally leads to a bipolarisation of political life (Duverger’s Law) or at least to the conclusion of pre-electoral agreements between large and small parties. Moreover, opting for a single round ballot magnifies, virtually systematically, the dominance of the majority party in terms of votes and under-representation of other parties in the assemblies. This trend is even more marked where there is a multi-member ballot.

Moreover, where there is a single-member first-past-the-post system in which two parties are virtually of equal strength (two-party system), the distribution of seats approximates to a cubic relationship (Law of Cubic Proportions):

S1/S2= (V1/V2)³

in which S1 = number of seats obtained by party 1, S2 = number of seats obtained by party 2
V1 = number of votes obtained by party 1, and V2 = number of votes obtained by party 2.

It should be noted however that there are numerous exceptions to this rule. Two conditions have to be fulfilled in order for this law to apply: all the constituencies must be substantially equal and the difference between the votes cast for the majority and the minority has to be virtually identical in all constituencies. As a result, the Law of Cubic Proportions can provide only an imperfect indication as to the possible make-up of assemblies.

b. Two-round ballots: a second round of voting is habitually used where the leading candidate or list failed to obtain an absolute majority in the first round and this type of majority is necessary in order to be declared elected in the first round. It is therefore closely linked to the majority system.