Evidence of a winning-cohesion tradeoff under multi-winner ranked-choice voting

New interest in "multi-winner ranked-choice voting" raises old questions about effects on party cohesion. Earlier scholars thought this single transferable vote (STV) rule was net-problematic for parties. This paper consults the roll-call and electoral records in Cincinnati (1929-57) and Worcester, Mass. (1949-60), two of three American STV implementations that produced conventional wisdom. First, I show how party cohesion could be high or low. Then I show how low-cohesion terms followed elections in which candidates campaigned for themselves over their parties. Finally, I show that parties endorsed such candidates when they needed the votes to expand their seat shares. In sum, the data suggest a strategic environment in which majority-seeking parties reach beyond their traditional bases - potentially at the expense of legislative cohesion. Whether that is good or bad depends on the value we give to cohesion.