Economic Quarterly

We provide an analysis that parses out the conditions under which diffusion indices based on disaggregated information are informative about overall economic activity. Building on work by Pinto, Sarte, and Sharp (2015), we highlight the fact that diffusion indices, appropriately scaled, capture contributions of changes in the extensive margin — e.g. how many sectors are growing or declining rather than by how much individual sectors are growing or declining — to aggregate growth. In the Fifth Federal Reserve District, for example, this margin captures the bulk of variations in aggregate employment growth. We then show that the Fifth District employment index, produced in real time using firm-level surveys, closely tracks a synthetic diffusion index constructed ex post using observed data. However, we also underscore that diffusion indices have their limitations. In the Fifth District, for example, the growth rate of average wages (relative to its mean) is frequently of a sign opposite to that indicated by changes in the extensive margin. Finally, we explore some of the implications of producing diffusion indices at a more localized level.