The variable that a scientist changes in an experiment is called the independent variable.

Here's why:

* Independent Variable: This is the factor that the scientist *manipulates* or changes on purpose. They are testing how this change affects something else.

* Dependent Variable: This is the factor that is being *measured* or observed. The scientist wants to see if the independent variable has any effect on this.

Example:

Let's say a scientist wants to see if fertilizer affects plant growth.

* Independent Variable: Amount of fertilizer used (the scientist changes this)

* Dependent Variable: Height of the plants (the scientist measures this to see if it changes)

Let me know if you'd like more examples!