The underground economy and other nonpriced production make it difficult to accurately measure the precise level of GDP. But GDP could still be very accurate for measuring changes in the economy.
If Janet Yellen, the Federal Reserve head, is trying to find out whether the U.S. economy has gone into a recession, are the difficulties of measuring nonpriced production likely to be important problems for her purposes?
How is this like always wearing your shoes when you step on the bathroom scale?