Demographic stage associated with a declining population size

Late-transitional

Explanation:

The stage

The demographic stage that is associated with a declining population size is "late-transitional". In late-transitional, the birth rates start to decline and decrease and therefore, the rate of population growth decelerates and decreases.

Some factors that may lead to this stage are access to contraceptive (family planning available), changing status of women, fewer families participating in agriculture, mechanized system leading to few workers, etc.