The national activity index surprised on the downside in August, when it came in at minus 0.16, down from a downwardly revised 0.07 level in July. The 3-month average was little changed at minus 0.14 versus minus 0.15 the previous month.

All four categories had a negative contribution, as production and income (minus 0.02 after a positive 0.12 in July), as well as personal consumption and housing (minus 0.08 after 0.03) turned negative in August. The employment-related index was unchanged at minus 0.04, and the sales, orders, and inventories category came in at minus 0.03, a slight improvement from minus 0.04 in July.

The national activity index is expected to rise further to 0.15 in August versus a higher-than-expected 0.12 in July that benefited from a jump in industrial production.

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.