What does a quantity index measure?

A quantity index measures the change in a quantity figure over a period of time, which provides insight into variations in the amount of goods produced or consumed. This type of index allows businesses and economists to analyze trends in production or consumption levels, independent of price changes.

The focus on how quantities evolve over time helps in assessing economic performance and making decisions related to inventory, production planning, and resource allocation. When analyzing changes in the quantity produced, for instance, companies can identify patterns that inform their operational strategies.

Other options consider different aspects: measuring the change in price pertains to a price index, while the volume of goods produced offers a snapshot rather than a change perspective. The rate at which items are sold relates more to sales velocity than to quantity changes over time. Thus, the correct answer highlights the specific function of a quantity index as it tracks variations in quantities systematically.