Final answer:
The National Income Approach is a method of measuring GDP by summing up all economic income, including labor wages, rentals, interest, and profits, over a year.
Step-by-step explanation:
Measuring GDP as the total economic gains in labor, rentals, interest, and profits is called the National Income Approach. This method involves summing up all the incomes produced in a year, specifically those from wages and salaries for labor, interest and dividends for capital, rent for land, and profit to the entrepreneur. This composition reflects the idea that all sales of the final goods and services that make up GDP will eventually end up as income for workers, managers, and owners of firms. Consequently, the sum of all this income is equated with national income (Y), which at times may be referred to as real GDP in inflation-adjusted terms.