# AP Statistics : How to identify dependent variables

## Example Questions

### Example Question #128 : Statistical Patterns And Random Phenomena

Which of the following represents a continuous variable?

The concentration of DNA in a liquid sample.

None of these.

The weight of footballs.

Two of these.

The number of fish in aquariums.

Two of these.

Explanation:

A continuous variable may assume an infinite number of different values between two given points while a discrete variable may only assume a specific number of specific values between two given points. Given this information, it becomes apparent that the concentration of DNA in a liquid sample and the weight of footballs are both continuous variables.

### Example Question #1 : How To Identify Dependent Variables

A hair care company is testing a new shampoo formula for its ability to keep hair clean for longer thanks to a new chemical compound XYZ that should limit oil production.

To test the appropriate strength of the shampoo, they are testing several concentrations of chemical XYZ to and measuring the amount of oil on the participant's scalp after 24 hours. The color of the shampoo will be randomly changed to keep the participants from knowing what shampoo is which strength.

Which of the following is the Dependant variable?

Shampoo Color

Gender

Amount of Oil on Participant's Scalp

Length of Participant Hair

Concentration of Chemical XYZ in shampoo

Amount of Oil on Participant's Scalp

Explanation:

The Independent variable is what the experimenters are directly manipulating-- here, that is the strength of the Chemical XYZ.

The Dependent variable is the variable that changes based on the Independent variable-- in this case, it is the amount of oil on participants' scalps.

### Example Question #2 : How To Identify Dependent Variables

A group of student researchers want to test the impact of temperature and lighting on the amount of food laboratory rats will eat.

To do this, they will first vary the room temperature (Hot or Cold) and see how much the lab rats eat at each temperature.

They will then vary the lighting (On or Off) and see how much the lab rats eat during each lighting state.

Which of the following is the Dependant Variable?

The number of rats

Room Temperature

Mouse Food Intake

Room Lighting

Mouse Food Intake

Explanation:

A Dependent variable is what changes based on the independent, manipulated variable.

The Independent variables are the Room Temperature and the Lighting state, which the researchers were manipulating themselves.

The Dependent variable is the Mouse Food Intake, which is the variable that changed based on how the independent variables changed.