Walter Russell Mead writes:

The most important story to come out of Washington recently had nothing to do with the endless presidential campaign. And although the media largely ignored it, the story changes the world.

The story's unlikely source was the staid World Bank, which published updated statistics on the economic output of 146 countries. China's economy, said the bank, is smaller than it thought.

About 40% smaller.

China, it turns out, isn't a $10-trillion economy on the brink of catching up with the United States. It is a $6-trillion economy, less than half our size. For the foreseeable future, China will have far less money to spend on its military and will face much deeper social and economic problems at home than experts previously believed.

What happened to $4 trillion in Chinese gross domestic product?

Statistics. When economists calculate a country's gross domestic product, they add up the prices of the goods and services its economy produces and get a total -- in dollars for the United States, euros for such countries as Germany and France and yuan for China. To compare countries' GDP, they typically convert each country's product into dollars.

The simplest way to do this is to use exchange rates. In 2006, the World Bank calculated that China produced 21 trillion yuan worth of goods and services. Using the market exchange rate of 7.8 yuan to the dollar, the bank pegged China's GDP at $2.7 trillion.

That number is too low. For one thing, like many countries, China artificially manipulates the value of its currency. For another, many goods in less developed economies such as China and Mexico are much cheaper than they are in countries such as the United States.