# Statistics and Probability Dictionary

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### Factor

In an experiment, the factor (also called an independent variable) is an explanatory variable manipulated by the experimenter.

Each factor has two or more levels, i.e., different values of the factor. Combinations of factor levels are called treatments. The table below shows independent variables, factors, levels, and treatments for a hypothetical experiment.

 Vitamin C 0 mg 250 mg 500 mg Vitamin E 0 mg Treatment 1 Treatment 2 Treatment 3 400 mg Treatment 4 Treatment 5 Treatment 6

In this hypothetical experiment, the researcher is studying the possible effects of Vitamin C and Vitamin E on health. There are two factors - dosage of Vitamin C and dosage of Vitamin E. The Vitamin C factor has three levels - 0 mg per day, 250 mg per day, and 500 mg per day. The Vitamin E factor has 2 levels - 0 mg per day and 400 mg per day. The experiment has six treatments. Treatment 1 is 0 mg of E and 0 mg of C, Treatment 2 is 0 mg of E and 250 mg of C, and so on.