Final answer:
The central phenomenon indicates the main variable studied, and population represents the group of interest in a research context. The provided example of a psychologist's study on the effect of tableware size on food consumption by college students is experimental research, defining how key components such as population, sample, and experimental units are identified within it.
Step-by-step explanation:
The central phenomenon of interest in a study often implies the main subject or variable that is being examined, while the population denotes the overall group of individuals that the researchers are interested in. In the context of the given examples, we are dealing with various research methodologies within psychology. The study provided where a psychologist examines the effect of tableware size on food consumption by college students is an example of experimental research. Here, the population is all college students, the sample includes the 100 college students in the study, and the experimental units are each individual student participant. The explanatory variable is the size of the tableware, the treatment is the use of tableware that is 20 percent smaller than normal, and the response variable is the amount of food eaten by the students.