Understanding the Factors that Affect the Incidence of Bellwether Counties: A Conditional Probability Model

Abstract

We update previous work on bellwethers in U.S. presidential elections. Comparing the most recent elections (2000-2020) to those in earlier periods (1960-1980), we see a striking decline in the proportion of bellwethers. We provide a model linking this decline to conditional probability calculations that recognize that (a) a county’s predictive success likelihood varies depending upon whether the winning candidate is going to be a Democrat or going to be a Republican; (b) as polarization rises, the number of potential bellwethers declines; and (c) election competitiveness can matter, but closer elections do not guarantee a greater likelihood of bellwethers. Indeed, we now have very close elections but a very low likelihood of bellwethers.