Factor (1 of 2)

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A factor is an independent variable. If an experiment is testing the effect of drug dosage, then "drug dosage" is a factor. Some experiments have more than one factor. For example, if the effect of drug dosage and age were both manipulated in the same experiment, then these two variables would be factors. The experiment would be called a two-factor experiment.

Between-Subjects Factor
A factor is a "between-subjects" factor (sometimes called a "between-subjects variable") if a different group of subjects is used for each level of the factor. For instance, consider an experiment comparing three levels of drug dosage (50 mg, 100 mg, and 150 mg). If the 50 mg dose were given to one group of subjects, the 100 mg dose to a second group, and the 150 mg dose to a third group, then a different group of subjects would be used for each level of the factor "drug dosage." This would make drug dosage a between-subjects factor.