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

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.