vary

Variables are factors that researchers observe in a research study. They observe and measure these factors in order to see how they change - increase or decrease - under specific conditions.

Researchers wanted to see which variables reduce students' concentration in class.

First they asked a class of students how many hours they sleep at night. Then they asked students if they find it hard to concentrate in class.

The researchers found that not enough sleep was an important variable: Students who slept for less than six hours at night could not concentrate in class the next day.