It's fun that certain flavors of (financial) economists are absolute zealots when it comes to DiD, identification strategies, instrumental variables...and then use "total revenues" from Compustat to calculate industry concentration. A short 🧵 Wharton did the world a service in creating WRDS to stitch together the unholy mess that was Compustat with CRSP and other data sources. Mostly it gets things right. (I'm pretty sure it correctly considers the original predecessor to JP Morgan Chase to be Manufacturers Hanover.)

Quibbling about the definition of “firm” is not necessarily an annoying digression, because the tech we have now makes the firm-like thingies we encounter perplexing. Definitions that might have been adequate 40 years ago may not work today. The field of economics is surprisingly bad at coming up with connotative definitions of firms, often referring to firms denotatively as “the basic productive units in an economy.” (So, not persons, or households, which are arguably productive units?)