Which of the following would an index help measure?

An index serves as a quantitative measure that allows for the comparison of different data points against a standard, providing insights into relative performance over time or across different entities. In the context of market penetration, an index can effectively quantify the extent to which a product or service is utilized within a specific market compared to its total available potential.

By measuring market penetration, an index can indicate whether a company's product is gaining traction among consumers and how it stands relative to competitors or historical data. It encapsulates the percentage of the target market that is actually buying or using the product, which is particularly valuable for evaluating marketing effectiveness or identifying growth opportunities.

The other choices do not reflect the primary function of an index. Total sales is a straightforward numerical figure without an index implication, market norms pertain to qualitative benchmarks and standards within an industry rather than quantitative metrics, and average price indicates a single data point rather than a comparative measure. Therefore, an index’s role in measuring market penetration makes it a crucial tool for understanding and analyzing market dynamics.