Replication Data for: Party system types and the decline of systemness in Western Europe: are party system classifications still useful?

Party system classifications have been central in political science, especially until Sartori’s influential typology in 1976. However, recent years have seen diminished attention to such classifications. Western European party systems have significantly transformed, particularly over the last 15 years due to multiple crises, affecting their core structure, or what Sartori termed ‘patterns of interparty competition’. This raises questions about whether these changes have undermined the very concept of systemness, making classifications irrelevant. This research note redefines party systems based on the number and composition of relevant political poles (governing alternatives) and, through a long-term analysis of Western Europe (20 countries since 1945), assesses their degree of systemness. Results indicate that many systems have become ‘non-systems,’ with fluctuating and unstable party poles. Most Western European systems have exhibited this ‘non-system’ type for at least half of legislatures since 1989, thus making classifications only short-lived snapshots and inevitably useless for long-term accounts.