This seems counterintuitive, but turns out that as infant mortality is reduced, population sizes also decrease, because parents don't need to anticipate that their babies are going to die.
Ini agak bertentangan, tetapi hasilnya ialah apabila kadar kematian bayi berkurangan saiz penududuk juga berkurangan, sebab ibu bapa tidak perlu menjangkakan yang bayi mereka akan mati.