Each of these four fields studies people, but they collect very different kinds of data, and that difference points to the answer.
- Demography: This field collects and analyses numerical data, such as birth rates, death rates, and age distribution, to describe and predict how a population changes. This numbers based approach is the scientific method the question is describing.
- Anthropology: This gathers information about customs, beliefs, and ways of life across human societies, which is a cultural rather than statistical approach.
- Sociology: This looks at social behaviour and relationships between people in groups, again a behavioural rather than purely statistical focus.
- Ecology: This studies the relationship between organisms, including humans, and their surroundings, and is not centred on human population statistics specifically.
Because the question specifically asks for the statistical study of human populations, demography is the discipline that fits.
Therefore, the correct answer is Demography.