Before revision:  I show that the commonly-used  linear-in-means ( LIM ) regression identifies a weighted sum of spillover effects with some negative weights, and that the difference in means between treated and controls identifies a combination of direct and spillover effects entering with different signs.
After revision:  I show that the commonly-used reduced-form linear-in-means ( LIM ) regression identifies a weighted sum of spillover effects with some negative weights, and that the difference in means between treated and controls identifies a combination of direct and spillover effects entering with different signs.