Demographers can predict when people are going to die but they have no way to predict how many children they will have. They have been getting it wrong for a l

Demographers can predict when people are going to die but they have no way to predict how many children they will have. They have been getting it wrong for a long time, assuming that the gradual decrease in birthrate will stop, only to be proven wrong. They can't just extrapolate assuming that birth rates will keep dropping since that would reduce the birthrate to 0. So they do the next best thing and assume it will stay constant. But in reality, we just don't know which way it will go.