Final answer:
In Dr. Margolas's study on the impact of sun lamp exposure on depression levels, 'depression levels' is best described as an operational definition. This refers to the specific measurement criteria used in the study to quantify the variable of depression.
The correct option is c.
Step-by-step explanation:
Dr. Margolas' examination of how daily exposure to a sun lamp in winter time impacts people's depression levels pertains to an operational definition. The depression levels in this context refer to a specific, quantifiable method of measurement that researchers use to define the variable being studied. In experimental research, such as Dr. Margolas's study, an operational definition ensures that variables are measurable and that the study can be replicated for consistency. The depression levels would be determined by predictable criteria, which might include scales for measuring mood, surveys, or questionnaires that have been validated for this purpose.
Given this information, the correct answer is c) operational definition, as it's the term that describes how researchers will measure depression levels in the study.