Weakness in production pulled the national activity index down from plus 0.14 in April to minus 0.15 in May. Reflecting a 0.2 percent fall in industrial production, the report's production component subtracted 0.09 from the headline. The sales, orders, and inventories component pulled the headline down 0.05 points with employment pulling it down by 0.03. The only positive was personal consumption and housing which added 0.02.

These result are confirmed by a minus 0.14 showing for the 3-month average which echo what have been weak indications from many economic readings, including leading indicators which will be updated at 10:00 a.m. ET this morning.

The national activity index is expected to hold steady in May at 0.08 versus 0.07 in an April report that showed noticeable improvement across components.

The Chicago Fed National Activity Index (CFNAI) is a monthly index that tracks overall economic activity and inflationary pressures. The CFNAI is a weighted average of 85 existing monthly indicators of national economic activity. It is constructed to have an average value of zero and a standard deviation of one. Since economic activity tends toward trend growth over time, a positive index reading corresponds to growth above trend and a negative index reading corresponds to growth below trend.

This index is unique among regional Federal Reserve Bank indexes in that it is national in scope. Investors are eager to have insight into economic growth and inflation. This index combines 85 diverse and already released indicators from four broad categories -- production and income; employment, unemployment, and hours; personal consumption and housing; and sales, orders, and inventories -- into an overall index to measure economic performance. The index provides another measure with which investors can measure overall growth.