Online job postings overstate labor market concentration by nearly a factor of three. That's the headline of a new NBER working paper with Michael Dalton and @ProfLisaBKahn . We match near-universal Burning Glass postings to the representative JOLTS and reweight them to line up with actual vacancies. The reason is simple: small and mid-sized establishments post online far less often, so measured HHIs look much too concentrated. Findings on the level and cyclicality of skill demand, by contrast, survive the adjustment — large employers account for most openings and are well covered. So: if your result rests on small employers, the coverage gap matters. nber.org/papers/w35697