P-Values on the Free-Slave State Border: A Critique of Bleakley and Rhode

Hoyt Bleakley and Paul Rhode use a “regression discontinuity design” (RDD) to find a persistent negative effect of slavery’s legality on rural population density throughout the period from 1790 to 1860. Yet their reported results cannot be replicated. Instead, the replication shows slavery’s negative effects only become statistically significant from 1840 onwards. Furthermore, the addition of an interaction term for slavery’s legality multiplied by longitude suggests that slavery may have facilitated the westward expansion of the Southern frontier in the antebellum period. This does not support the claim that slavery impeded the growth of American capitalism.