We've studied populations all over the world since the turn of the last century.

Scientists are studying different populations and relationships to try to learn more about the disease.

Demographers (people who study human populations) call this a natural population.

The participants recruited should reflect the diversity in the population being studied.

Classification of a disease's rarity also depends on the population being studied.

That is exactly what happened, in four local populations studied and treated over four years.

The population studied by the Census Bureau changed between 1990 and 2000, he said.

One way to reduce costs is by selecting smaller samples which hopefully represent the population being studied.

It is also necessary to study populations in which random use of antimalarial drugs does not occur.

The two studies cannot be directly compared because they relied on different methods to study different populations.