Abstract: The form of proportional electoral systems, and their nature, proportionality and impact on a party system are influenced by a multitude of factors. The factors that can be already set up while forming the electoral rules – factors that are independent of external circumstances – are called ‘variables’. In the case of the list PR systems there are four main variables: electoral district magnitude, electoral formula, legal threshold and the number and character of tier districting. Using these four basic variables in connection with proportional electoral systems it is possible to achieve almost any results or data output – from the most proportional to the most disproportional, with the potential to favour small, medium or even large parties. The variables can also lead to a favouring of parties based on their character, such as the measure of coalition potential or the geographic distribution of the electorate. This article presents the way in which these variable can work, explains their technical nature and their effects, and the way they interactwith each other, including their reciprocal interaction, crossing, and overlapping.
