Political parties are active when citizens choose among candidates in elections, and when winning candidates choose among policy alternatives in government. But the inextricably linked institutions, incentives, and behavior that determine these multistage choices are substantively complex and analytically unwieldy, particularly if modeled explicitly and considered in total: from citizen preferences through government outcomes. To strike a balance between complexity and tractability, we modify standard spatial models of electoral competition and governmental policy-making and develop a model to study how components of partisanship - such as candidate platform separation in elections, party-ID-based voting, national partisan tides, and party-disciplined behavior in the legislature - are related to outcomes that deviate systematically from a citizen-based central benchmark. Such deviation is called partisan bias. The study reveals that none of the party-in-electorate conditions is capable of producing biased policy outcomes independently. Specified combinations of conditions, however, can significantly increase the bias and/or the variance of policy outcomes, sometimes in subtle ways.
