Final answer:
Drug X is an independent variable in the study of its effects on anxiety levels. It is the factor being manipulated to observe the outcome on the dependent variable, which in this context is the anxiety levels.
Step-by-step explanation:
The researcher wants to know how Drug X affects anxiety levels. In this context, Drug X is an independent variable because it is the factor that is manipulated or changed by the researchers to observe its effects on anxiety levels, which would be the dependent variable. In experimental design, the independent variable is the one that is manipulated to test its effect on the dependent variable. An independent variable can also be conceptualized as a treatment in a controlled experiment.
In the example of the psychologist studying the effect of tableware size on food consumption, the population would be all college students, the sample is the 100 college students in the study, and the experimental units are each individual college student who participated. The explanatory variable is the size of the tableware, the treatment is the tableware that is 20 percent smaller than normal, and the response variable is the amount of food eaten.