CHICAGO, Jan. 28 (Xinhua) -- The Chicago Fed National Activity Index (CFNAI) rose slightly to +0.27 in December from +0.21 in November, indicating a mild growth of U.S. economy, the Chicago Federal Reserve Bank announced on Monday.

The index is a weighted average of 85 indicators of growth in national economic activity drawn from four broad categories of data: production and income; employment; personal consumption and housing; and sales, orders and inventories.

Two of the four broad categories of indicators that make up the index increased from November, and two of the four categories made positive contributions to the index in December.

The contribution from production-related indicators to the CFNAI increased to +0.22 in December from +0.02 in November.

Manufacturing industrial production rose 1.1 percent in December after edging up 0.1 percent in November. The sales, orders, and inventories category made a neutral contribution to the CFNAI in December, down from +0.12 in November.

The Institute for Supply Management's Manufacturing New Orders Index decreased to 51.1 in December from 62.1 in November.

Employment-related indicators contributed +0.11 to the CFNAI in December, up slightly from +0.10 in November. Total nonfarm pay rolls rose by 312,000 in December after increasing by 176,000 in the previous month.

However, the unemployment rate increased to 3.9 percent in December from 3.7 percent in November. The contribution of the personal consumption and housing category to the CFNAI edged down to -0.06 in December from -0.03 in November.