Which term describes the combination of many different items into a single economic variable?

The term that describes the combination of many different items into a single economic variable is aggregation. In economics, aggregation refers to the process of summing or combining various individual data points or components into a broader measure or index. This is commonly used in the analysis of economic indicators, such as gross domestic product (GDP), where various sectors of the economy or different types of goods and services are combined to provide an overall picture of economic performance.

The other concepts listed, such as investment, capital goods, and labor force, represent specific economic categories or factors but do not pertain to the action of combining different items into a single measure. Investment refers to the allocation of resources (typically money) towards the creation of goods or services. Capital goods are the physical assets that a company uses in production, and the labor force pertains to the pool of individuals who are available for work. Thus, aggregation is the relevant term that captures the essence of combining various economic items into one variable for analysis.