Granular Instrumental Variables

We propose a new way to construct instruments in a broad class of economic environments: "granular instrumental variables" (GIVs). In the economies we study, a few large firms, in- dustries or countries account for an important share of economic activity. As the idiosyncratic shocks from these large players affect aggregate outcomes, they are valid and often powerful instruments. We provide a methodology to extract idiosyncratic shocks from the data in order to create GIVs, which are size-weighted sums of idiosyncratic shocks. These GIVs allow us to then estimate parameters of interest, including causal elasticities and multipliers