Question

A kind of variable that a researcher purposely changes in an investigation is...

constant.
controlled.
dependent.
independent.

Answer 1

The independent variable, because the I.V. is what you wil change throughout your experiment.

Answer 2

The variable that researchers manipulate is the independent variable.

The reason for this is because in experiments different manipulations are often introduced. The sole purpose of these manipulations is to see whether they will affect our independent variable and if they will change its value.