Final answer:
Single-subject designs provide causal verification that behavior changes because of manipulation, which is the correct answer C) in the multiple-choice question.
Step-by-step explanation:
Single-subject designs provide causal verification that behavior change occurred because manipulation occurred and no other cause. The correct answer is C) Causal; manipulation. This type of design is meant to demonstrate that the manipulation of the independent variable by the experimenter is the cause of the observed change in the dependent variable.
In an ideal experimental design, subjects are assigned randomly to treatment groups to eliminate the problem of lurking variables. This random assignment helps ensure that the only difference between treatment groups is the one imposed by the experimenter, which means any difference in response must be due to the treatment itself. When a control group receives a placebo, and the experimental group receives the actual treatment, differences in responses between groups can be causally attributed to the treatment.
The example provided of the psychologist's study on the influence of tableware size on food consumption is a controlled experiment, where the size of the tableware is the independent variable, and the amount of consumed food is the dependent variable.