Read the following example and answer the questions that follow it. Dr. Jones conducts a research study investigating the effects of a new drug that is intended to reduce the craving for alcohol. A group of alcoholics who are being treated at a clinic is selected for the study. Half of the participants are given the drug along with their regular treatment, and the other half receives a placebo. Dr. Jones records whether each individual is still sober after 6 months.

a. Identify the independent variable in this study.

b. Identify the number of levels of the independent variable.

c. Identify the dependent variable in this study.

d. Assuming that the study includes participants ranging in age from 18 to 62 years of age, then which of the following most accurately describes the age variable in the study? (independent, dependent, extraneous, confounding)

e. If the participants in the drug group are noticeably older (on average) than the individuals in the placebo group, then which of the following most accurately describes the age variable in the study? (independent, dependent, extraneous, confounding)