Which U.S. economic indicator is only available on a quarterly basis?

Gross Domestic Product (GDP) is the correct answer as it is a key economic indicator that measures the total economic output of a country and reflects its economic health. GDP data is compiled and released quarterly, allowing for a periodic assessment of economic growth and productivity. This quarterly frequency is important for tracking trends over time, especially as economic conditions can change rapidly.

Other economic indicators mentioned, such as the Consumer Price Index, Nonfarm Payrolls, and Retail Sales, are available on a monthly basis. This more frequent release allows for timely insights into inflation, employment trends, and consumer spending, making them crucial for short-term economic analysis. In contrast, the nature of GDP measurement, which involves collecting and analyzing a wide range of economic data, necessitates a longer timeframe for compilation and reporting. Thus, GDP stands out among these indicators for its quarterly availability.