Swing (politics)
An electoral swing analysis (or swing) shows the extent of change in voter support, typically from one election to another, expressed as a positive or negative percentage. A multi-party swing is an indicator of a change in the electorate's preference between candidates or parties, often between major parties in a two-party system. A swing can be calculated for the electorate as a whole, for a given electoral district or for a particular demographic.
A swing is particularly useful for analysing change in voter support over time, or as a tool for predicting the outcome of elections in constituency-based systems. Swing is also usefully deployed when analysing the shift in voter intentions revealed by (political) opinion polls or to compare polls concisely which may rely on differing samples and on markedly different swings and therefore predict extraneous results.[1]
Labour to Conservative swing
Liberal Democrat to Conservative swing
Labour to Liberal Democrat swing
In the UK, a two-party swing (averaged model) is generally used, which adds one party's increase in share of the vote (expressed as a percentage point) to the percentage-point fall of another party, and divides the total by two.
Thus, if Party One's vote rises by 4 points and Party Two's vote falls 5 points, the swing is 4.5 points (Party 2 to Party 1).[7] For disambiguation, suffixes such as: (Con to Lab) (Lab to Lib Dem) (Lib Dem to Con) must be added where three parties stand. Otherwise, a problem when deciding which swing is meant and which swing is best to publish arises where a lower party takes first or second, or where a party loses one of the top two places.[n 1]
Originating as a mathematical calculation for comparing the results of two constituencies,[n 2] any of these figures can be used as an indication of the scale of voter change between any two political parties, as shown below for the 2010 United Kingdom general election:
Three party swing or greater[edit]
Some websites provide a pie chart based or column-based multi party swingometer where ± x%, ± x%, ± x% and so on is displayed or can be input for three parties (or more in more plural democracies). This tool or illustration provides likely outcomes wherever more than two political parties have a significant influence on which politicians are elected.[8] In multiparty systems exit polls frequently include a question as to voting behavior in the last applicable election. Based on those exit polls "voter migration" (where vote gains for a specific party came from and losses of another went to) analyses are published and discussed in election coverage.