Which of the following metrics provides insight into global stock market sizes?

The metric that provides insight into global stock market sizes is STAT. This metric is used to analyze and compare the overall scale of various stock markets across different countries or regions. It helps investors, analysts, and financial professionals understand the relative size and significance of these markets, which can be crucial for portfolio diversification, investment strategy formulation, or economic analysis.

Other options like RVR, HDS, and OWN serve different purposes in financial analysis. RVR typically relates to relative volatility measurements, HDS can pertain to historical data services, and OWN may deal with ownership structures of securities, which are not specifically designed to give a picture of stock market sizes globally. Understanding the utility of these metrics ensures that one can effectively analyze market data for informed decision-making.