There are several elements of electoral systems that may influence political parties in their magnitude, organisation, and campaigning and the opportunities for independent candidates in a political system.
One of the most important factors is the electoral system’s ability to translate votes cast into seats won proportionally. Determining this is to a large extent the district magnitude, which is the number of members to be elected in each electoral district.
Under a Plurality/Majority system such as FPTP, AV, or the Two-Round System, there is a district magnitude of one; voters are electing a single representative.
By contrast, all PR systems, some plurality/majority systems such as Block Vote and PBV, and some other systems such as Limited Vote and SNTV, require electoral districts which elect more than one member. Under any proportional system, the number of members to be chosen in each district determines, to a significant extent, how proportional the election results will be.
There is generally a strong positive correlation between average district magnitude and average party magnitude. The party magnitude is an important factor in determining who will be elected. If only one candidate from a party is elected in a district, that candidate is likely to be male and a member of the majority ethnic or social group in the district. If two or more are elected, balanced tickets may have more effect, making it likely that more women and more candidates from minorities will be successful.
Different kinds of electoral system are likely to encourage different kinds of party organisation and party system.
Highly centralized political systems using closed-list PR are the most likely to encourage strong party organisations; conversely, decentralized, district-based systems like FPTP may have the opposite effect. The type of electoral system may influence the type of party system that evolves. The FPTP system, for instance, mostly sustains a party system that consists of two major parties, often gravitating towards a party on the left and one on the right, alternating in power. Proportional Representation Systems, on the other hand, encourage the formation of several political parties, thereby better reflecting the policy, ideology, or leadership differences within society.
The electoral system design is crucial for the understanding of the position of individual candidates in the political system as a whole. Different kinds of electoral systems result in different relationships between individual candidates and their supporters. In general, systems which make use of single-member electoral districts are seen as encouraging individual candidates to see themselves as the delegates of particular geographical areas and beholden to the interests of their local electorate. By contrast, systems which use large multi-member districts, such as most PR systems, are more likely to deliver representatives whose primary loyalty lies with their party on national issues.
The electoral system design can influence the way a party campaigns and the way political elites behave. Proportional representation list systems, where voters choose between parties and policy programmes, are said to foster campaign centralization. Proportional representation systems also encourage parties to campaign beyond the districts in which they are strong, because the political parties aim to increase their overall votes regardless where the votes come from. In Plurality/Majority Systems, on the other hand, voters tend to choose between candidates rather than among political parties and programmes. In a single-member-district system, the campaigning would focus on that particular candidate.
Additionally, under a Plurality/Majority system, a party may practically abandon its campaign in a district where it sees no chance of winning.
