A measure of future U.S. economic growth fell to a six-week low in the latest week, while the index’s annualized growth rate rose to an 18-week high, a research group said on Friday.

The Economic Cycle Research Institute, a New York-based independent forecasting group, said its Weekly Leading Index fell to 122.1 in the week ended October 15 from 122.2 the previous week.

That was the lowest since September 3, when it stood at 121.9.

The index’s annualized growth rate rose to minus 6.8 percent from minus 7.0 percent a week earlier. That was the highest since June 11, when it stood at minus 6.1 percent.

Occasionally the index level and growth rate can move in different directions, because the growth rate is derived from a four-week moving average, the research institute said.