National parties and group membership in the European Parliament: ideology or pragmatism?

This contribution investigates the factors behind political group membership in the European Parliament. In June 2009, more than 150 national parties, from the 27 member countries, joined one of the seven transnational groupings. Two main explanations for group membership are advanced. A first, traditional argument is based on the ideological or policy compatibility of the member parties. National parties will join the political group that best matches their programmatic position. A second argument focuses, instead, on the structure of incentives in the Parliament, positing that the pragmatic goals of national parties are better advanced by joining the largest and most influential groups. These arguments are tested by fitting a multinomial logit model for political group 'choice' based on the 2009 Euromanifestos data. The findings suggest that ideological compatibility is the most important factor behind transnational affiliation, even if some caution is needed for the 'new', post-communist members.