A golfer wants a new set of clubs to improve her game. In an experiment, she tests different drivers made from different materials. She compares the drivers to the distance of her shot. In this simple experiment, the independent variable is the

type of material used to make the club head

Explanation:

Independent variable: In research methods, the term "independent variable" is described as a variable that is being changed or controlled by an investigator or researcher in an experiment in order to see its effects on the dependent variable as it is responsible for affecting the dependent variable directly.

In the question above, the independent variable is "type of material used to make the club head".