Which of the following metrics is used to compare economic performance across different countries?

The metric that is commonly used to compare economic performance across different countries is typically referred to as the Economic Freedom Index or variations of it. The chosen answer is aligned with various international methodologies or indices that assess and rank the economic performance of nations based on criteria such as productivity, trade balances, and overall economic growth.

While other options may represent specific frameworks or models used for different applications in economics, they do not hold the same weight in the context of cross-country economic comparison. Metrics like GDP per capita, Human Development Index (HDI), and Purchasing Power Parity (PPP) are often derived or influenced by the concepts similar to the chosen choice, but this specific option encapsulates the broader evaluation of economic freedom, which significantly impacts the comparative analysis of economic performance on a global scale.

This makes the selected answer particularly relevant, as it directly pertains to standardized assessments of economic conditions that allow for insightful comparisons between the economic environments of various nations.