Final answer:
Macroeconomics focuses on measuring the economy through indicators like GDP to assess the overall performance of the economy in terms of output and price level.
Step-by-step explanation:
Economists generally express the size of a nation's economy as its gross domestic product (GDP), which measures the value of the output of all goods and services produced within the country in a year. GDP is measured by taking the quantities of all goods and services produced, multiplying them by their prices, and summing the total. It reflects the overall performance of the economy by examining total output, the price level, and other aggregate measures.