Independent and Dependent Variables

Definition

• In an experiment, the independent variable is the variable that is varied or manipulated by the researcher, and the dependent variable is the response that is measured.

Example Number 1

• Independent Variable: A scientist studies the impact of a drug on cancer. The independent variable is the administration of the drug.

• Dependent variable is the impact the drug has on cancer.

• You can vary the independent variable and see what happens to the dependent variable. For instance, you could vary the dose and see how the increased or decreased dose affects the cancer.

Example 2

• A scientist studies how many days people can eat soup until they get sick. The independent variable is the number of days of consuming soup.

• The dependent variable is the onset of illness.

Example 3

• If you conduct an experiment on the effect of talking on plant growth, the number of minutes you talk to the plant is the independent variable.

• The dependent variable is the amount that the plant grows.

Example 4

• The effect of temperature on E. coli bacterial growth.

• Independent variable (varied by the researcher) is temperature.

• Dependent variable is the rate of the growth of E. coli bacteria.

Example 5

• The effects of touch (pressure) on the firing of neurons in Aplysia californica.

• Independent variable is the intensity of the “touch.”

• The dependent variable is the intensity of neurons firing.