Not worth worrying about given context of imminent ASI.
This is something that confuses me as well: why do a lot of people in these circles seem care about the fertility crisis while also believing that ASI is coming very soon?
In both optimistic and pessimistic scenarios about what a post-ASI world looks like, I’m struggling to see a future where the fact that people in the 2020s had relatively few babies matters.
I would be very surprised if this FVU_B actually another definition and not a bug. It’s not a fraction of the variance and those denominators can easily be zero or very near zero.