How Do Interest Groups Influence Elections? Evidence from British Trade Unions 1900-2019

Abstract

Trade unions sponsored the political campaigns of candidates running for office in many countries throughout the 20th century. Yet little is known about the electoral consequences of these sponsorship arrangements. I study how union sponsorship affected the electoral performance of parliamentary candidates in Great Britain (1900-2019). On the basis of archival material, I collect new data on universe of union-sponsored candidates, and new data on all parliamentary candidates and their electoral campaigns. Employing a series of difference-in-differences designs, I examine how sponsorship affected candidate nominations and general elections. The results show that attaining a union sponsorship increases the probability that a candidate wins the nomination in an electorally attractive constituency. Second, sponsorship causes an inflow of financial and human resources into constituencies, engendering a professionalization of political campaigns and party organizations. Third, union sponsorship approximately causes a six-percentage-point increase in the average candidate's vote share, and two-thirds of this advantage is driven by nomination in better constituencies, while campaign spending account for the remaining boost in performance. Finally, heterogeneity in the treatment effect indicates that the electoral influence of unions is strongest in time periods and in industries where substantial government interventions affected the labor market.