Final answer:
The 'daily sun lamp exposure' represents the operational definition in Dr. Margolas's research, describing how to measure the variable that is hypothesized to influence depression levels.
Step-by-step explanation:
When Dr. Margolas examines how daily exposure to a sun lamp in winter time impacts people's depression levels, the 'daily sun lamp exposure' could be considered an operational definition. An operational definition in research specifically outlines the measurement of a variable. In this case, it quantifies the 'daily sun lamp exposure,' which could be defined in terms of duration (minutes or hours per day), intensity (e.g., wattage of the lamp), or both. This operational definition enables the researcher to test the hypothesis, which is a prediction about the relationship between the sun lamp exposure and depression levels. The variable in question, daily sun lamp exposure, is what the researcher manipulates to observe the effect on depression levels, a dependent variable.