Australian Politics and Policy - Senior, 2019a

Electoral systems
Figure 2 Australian House of Representatives – ‘two-party preferred’ election results, 1949
to 2016. Source: AEC 2016.
have the opposite problem: their key strength is in representing views across the
ideological spectrum, but they often suffer from political instability.
Consensual systems
In almost all of South America, and northern, central and western Europe, voters
elect more than one candidate to represent their electoral division. Instead of one
local member, they might have two, three or more. The number of representatives
in each district is called district magnitude, andwhileitmayseemasmallthing,
it has a large effect on electoral outcomes, the number of parties that contest
elections and win seats, the stability of governments and the kinds of policies that
the legislature and government produce.
According to Duverger’s Law, parties with similar ideological positions will
inevitably either merge or withdraw from elections to avoid stealing votes from
each other and allowing ideologically distant parties to win. In multi-member
districts (i.e. where the district magnitude is two or higher), ideologically similar
parties or candidates can both nominate for election and plausibly be elected. They
may still ‘steal’ votes from each other, increasing the total vote share of a common
political opponent, but as the vote share required for winning is lower the chance
of either or both candidates winning at least one seat is higher.
Imagine a local election in which five members are being chosen to represent
one division. There are 20 candidates nominated: five centre-left candidates, five
centre-right candidates, five candidates from the far left and five candidates from
the far right. In a plurality (‘first past the post’) election, the far left and far right
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