CHICAGO, Dec. 28 (Xinhua) -- The Chicago Purchasing Managers Index (Chicago PMI), also known as Chicago Business Barometer, dropped 1.0 point to 65.4 in December as concerns over tariffs continued to stir uncertainty.

The Chicago PMI eased slightly following an eight-point surge last month, according to a statement released Friday by the Institute for Supply Management Chicago.

The barometer is made up of production, new orders, order backlogs, employment and supplier deliveries indicators and is designed to predict future changes in U.S. gross domestic product.

It is considered to be a leading indicator of the U.S. economy, because the Chicago region somewhat mirrors the United States overall.

Contributing to December's moderation was a fall in demand. However, November's order book strength did translate into higher output this month with production rising to an 11-month high.

Recently, many U.S. companies have voiced their concerns over higher tariffs due to unsolved trade disputes with China. Firms reported customer pressure for earlier delivery on existing orders to avoid possible tariff hikes.

Order backlogs rose for a second straight month, hitting a five-month high, further reversing October's fall.

Supply-side issues remained a hinderance, with the supplier deliveries indicator fell to its lowest level in a year this month.

After two consecutive months of higher readings, the employment indicator retreated in December, although remained above the neutral-50 mark.

"The MNI Chicago Business Barometer saw 2018 out in good health, assisted by a firm uptick in production, cementing the best calendar quarter outturn in a year," said Jai Lakhani, Economist at MNI Indicators, which compiles data for Chicago PMI on behalf of the Institute for Supply Management Chicago.

"Still, concerns over tariffs continue to linger in the background and stir uncertainty," he added.