A Better ZIP5-County Crosswalk

I use a healthcare expenditure dataset with observations geographically coded at the 5-digit zipcode level, but I'd also like to know which county an observation 'belongs' to. Maybe I want to cluster standard errors by county, or control for county-specific trends. You'd imagine this would be straightforward, but I haven't yet found a government crosswalk … Continue reading A Better ZIP5-County Crosswalk