[jampekka]

Per abstract it's a "a dynamic difference-in-differences" analysis, which means likely that they see whether the employee behavior changes after the event. But establishing causation with it still requires quite a few assumptions.

PNAS is kinda known for headline grabbing research with at times a bit less rigorous methodology.

https://statmodeling.stat.columbia.edu/2017/10/04/breaking-p...

> Certainly they took the time to perform a controlled experiment and assigned managers at random to deliver the birthday cards late or on time. That would be cheap to do and minimally invasive for the human subjects.

If the results are true, it would be actually quite expensive because of the drop in productivity. It could also be a bit of a nightmare to push through ethical review.

[dmurray]

They could start by observing the rate at which birthday cards are delivered on time, and not vary too much from that.

I suppose the impact on productivity isn't known in advance, and it might be that failing to receive a birthday card from a normally diligent manager costs the company more in productivity than it gains from a sloppy manager unexpectedly giving one on time.