Electoral volatility in the European Parliament, caused by vote switching between parties that enter or exit from the party system. A party is considered as entering the party system where it receives at least 1% of the national share in election at time t+1 (while it received less than 1% in election at time t). Conversely, a party is considered as exiting the part system where it receives less than 1% in election at time t+1 (while it received at least 1% in election at time t).