On mismeasurement of strategic voting under mixed member electoral systems

Under mixed systems, voters cast two votes to elect the same legislative body: one vote for parties using proportional rules and one for candidates using majoritarian rules. Voters are said to cast straight-tickets if the candidate they vote for is of the same party as their proportional vote; otherwise, they are said to cast split-tickets. Split-ticket voting is commonly used as a measure of strategic voting as splitters are usually assumed to express their true preference in one vote but vote strategically in the other. This study challenges this practice showing that split-ticket voting does not necessarily indicate strategic voting, just as straight-ticket voting does not necessarily indicate a sincere vote. This result has wider consequences as it indicates that measuring strategic voting from observed behaviour can result in incorrect conclusions about vote choice.