FRANCES E. LEE AND BRUCE I. OPPENHEIMER
Senate Apportionment: Competitiveness and Partisan Advantage
Legislative Studies Quarterly XXII:3-24

This paper examines two unanticipated consequences of the equal representation of states on Senate elections-competitiveness and partisan advantage. Using a fixed-effects (LSDV) model that controls for important intervening variables to test the hypothesis that variation in state population size affects the competitiveness of Senate elections, we find a far stronger relationship between state population and electoral competitiveness than have previous works. In addition, Senate apportionment has had implications for the partisan composition of the Senate. When we compare the actual outcomes of Senate elections over time with hypothetical outcomes, which we derive by holding state population constant, we find that Senate apportionment has had important consequences for the partisan composition of the Senate in several periods. From the mid-1970s until (but not including) 1994, Senate apportionment enabled Republicans to hold seats disproportionate to their party's share of the national Senate vote.