That’s about in line with the 10-year or three generations rule that the IUCN currently uses to model changes. But that doesn’t mean it’s necessarily sufficient. “It’s not really about the species, or generation time of a species, but how variable a species is from year to year,” White says. “For example, if you have a small mouse species that varies a lot per year, you could sample for a short amount of time and draw the wrong conclusion.” Based on his results, Whites says that each species really has to be modeled individually, using empirical results, or even similar species to create population models. And even with that level of evidence, extinction is still a difficult case.