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In an experiment, the factor
(also called an independent variable) is an explanatory
variable manipulated by the experimenter. Each factor has two or more
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.
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.