In experimental research, it is convenient to classify variables as either independent variables or dependent variables. The independent variable, also called the predictor variable, is the variable that is manipulated by a researcher. The dependent variable, also called the response variable, is the response that is measured or observed. Consider an experiment to evaluate the effectiveness of two nonnicotine medications in stopping tobacco use among young adults. One hundred adults are randomly assigned to take either varenicline (Chantix) or bupropion (Zyban) tablets. In this experiment, the variable that is manipulated by the researcher is the type of medication. The dependent variable is the proportion of adults who no longer use tobacco at the conclusion of the experiment.

Independent and dependent variables can be classified as either ...