Group collapse and strategic switching: why MEPs change their affiliations in the European Parliament

It is relatively common for MEPs to change their political group in the European Parliament, but what explains this behaviour? Drawing on a new study, Aaron R. Martin writes that while group switching is often assumed to be a strategic choice, over half of the switches that took place in the European Parliament between 1979 and 2009 were non-strategic moves triggered by the collapse of an existing group.