Countries are classified into income categories based on their economic productivity using metrics such as Gross Domestic Product (GDP) and ________, which takes into account the income received by residents from abroad.

Countries are classified into income categories based on their economic productivity by looking at their Gross Domestic Product (GDP) and Gross National Income (GNI). GDP measures the total value of goods and services produced within a country, while GNI includes the income earned by residents from abroad, such as investments or wages. This means that GNI gives a fuller picture of the economic well-being of a country's citizens. For example, if a country has a high GDP but many of its citizens work overseas and send money back home, its GNI will show a different and often higher income level than GDP alone suggests. By using both metrics, we can better understand the true economic situation and living standards of people in different countries.