Union Success in Representation Elections: Why Does Unit Size Matter?

I establish four facts regarding the pattern of NLRB supervised representation election activity over the past 45 years: 1) the quantity of election activity has fallen sharply and discontinuously since the mid-70's after increasing between the mid-1950's and the mid-1970's; 2) union success in elections held has declined less sharply, though continuously, over the entire period; 3) it has always been the case that unions have been less likely to win NLRB-supervised representation elections in large units than in small units; and 4) the size-gap in union success rates has widened substantially over the last forty years. I develop a simple optimizing model of the union decision to hold a representation election that can account for the first three facts. I provide a pair of competing explanations for the fourth fact: one based on differential behavior by employers of different sizes and one purely statistical. I then develop and estimate three empirical models of election outcomes using data on NLRB elections over the 1952-98 time period in order to determine whether the simple statistical model can account for the size pattern of union win rates over time. I conclude that systematic union selection of targets for organization combined with the purely statistical factors can largely account for observed patterns.