The party system development in Central and Eastern Europe after the fall of the Berlin wall has put focus on the question what it takes for party systems in newly established countries to stabilize. Some scholars have argued that party system stabilization will follow more or less automatically as time elapse and democracy consolidates, whereas other have pointed to a number of factors which sustain the level of instability. In this paper we analyze party system stability in ten post-communist EU-member states 1990-2012. The study is based on data from the 68 parliamentary elections held since the first multiparty elections in 1990. We use three indicators to capture the extent of party system stability: electoral volatility, support for new and splinter parties and the number of parties entering or exiting parliament. The first aim of the paper is to compare the level of party system stability temporally as well as between the countries. The results show that the level of instability is consistently high in the region in almost all countries and that there are few indications of stabilization. Estonia and Poland are the only countries in which there is a stabilizing trend. The second aim of the paper is to explain the variations temporally and cross country. We will test a number of factors which may account for the differences, such as the socio-economic development and the level of corruption. We will also test whether the sustained instability is caused by what we call an asymmetric path dependency, implying that instability breeds further instability, because voters know that new parties have a good chance to make it all the way to the government and the political entrepreneurs know that voters are prone to support such parties. There is thus both a supply and demand for changing status quo.
