Mark Zandi: Why US economic growth isn't as strong as it looks

The US economy grew a surprisingly strong 3.2% in this year's first quarter, according to the latest real GDP estimate from the Bureau of Economic Analysis (BEA). This was about a percentage point more than expected by the consensus of economists who track this number. While a surprise, global investors didn't seem to care. Stock prices and interest rates hardly budged on the data. Why?