The Federal Reserve Board's data on industrial production are often badly misinterpreted. The error occurs for two reasons. First, there are often large revisions to the monthly data and second, the aggregate index is often moved by large changes in mining or utility output.

The data for March released yesterday gave us examples of both. Therefore the NYT missed the story when it gave us the ominous news that: 

"A Federal Reserve report showed American industrial output was flat for a second consecutive month in March, held back by a 0.2 percent drop in manufacturing."

While the manufacturing index did show a 0.2 percent decline in March, its February reading was revised up by 0.5 percent. Therefore the March reading stood 0.3 percent from the advanced report for February and 0.6 percent above the February level. The reason that the industrial production index as a whole was flat over this period was a decline in mining output of approximately 3.8 percent.