Using election returns, public opinion surveys, and legislative roll-call data from many mixed systems in every world region, the authors show that contamination systematically affects party strategy, voting behaviour, legislative cohesion and overall structure of partisan competition.

FEDERICO FERRARA is a PhD Candidate at Harvard University, USA. ERIK S. HERRON is Assistant Professor, Department of Political Science and Centre for Russian and Eastern European Studies, University of Kansas, USA. MISA NISHIKAWA is Assistant Professor, Ball State University, USA.