Final answer:
GDP, or Gross Domestic Product, is the most commonly-used economic metric for gauging a country's economic activity within its borders. It captures the total monetary value of goods and services produced in a given year, but doesn't capture international activities of a nation's firms and citizens, work done abroad, or metrics related to quality of life.
Step-by-step explanation:
Among the economic metrics mentioned, Gross Domestic Product (GDP) is generally regarded as the truest measure of economic activity within a country. GDP represents the total monetary value of all goods and services produced within a country's borders in a given year and stands as a straightforward way to categorize economies. However, GDP does not account for the value produced by a nation's businesses and labor abroad, unlike Gross National Product (GNP) which does include these activities and subtracts payments sent home by foreign labor and businesses in the country.
Gross National Income (GNI) offers a broader picture by encompassing total income generated by a nation over 12 months, including international activities, after expenses to other countries have been paid. Though GNI gives a sense of the actual money flow for a country, GDP is still more commonly used for measuring the health of an economy.
It is important to understand that GDP focuses on economic activity only, not capturing all the aspects of well-being or prosperity, as pointed out by economists like Kate Raworth. This limitation suggests that while GDP can serve as a proxy for economic strength, it is not a comprehensive measure of the overall quality of life.