Which economic measure is best used to assess a country's production level?

Real GDP is the best measure to assess a country's production level because it accounts for changes in prices due to inflation or deflation and reflects the true value of goods and services produced. By using constant prices, Real GDP allows for a more accurate comparison of economic output over time, indicating whether an economy is actually growing or contracting in terms of production.

Nominal GDP, while it measures the total monetary value of goods and services without adjusting for price changes, can misrepresent the actual production level if there have been significant fluctuations in prices. The GDP deflator is a measure of inflation rather than a direct measure of production, and GNP includes net income from abroad, which may not accurately reflect domestic production levels. Thus, Real GDP is the most reliable indicator for assessing a country's production capacity.