Human trafficking is an underground activity and the victims are referred to as a "hidden population."

"This is not just a hidden population," he said.

But as soon as it became clear that we meant to stay, the hidden population began to creep forth.

Locate hidden populations: It is possible for the surveyors to include people in the survey that they would not have known.

A new approach to the study of hidden populations.

We become a hidden population.

Uncovering hidden populations could hold the key to incorporating new genetics into the stagnant gene pool, and rebound the species to a healthy sustainable level.

The situation with the hidden population of older children from three to six years old, in other words the so-called little schools, is not much better.

Automated identification systems could potentially help findings of rare and hidden populations.