A measure of future U.S. economic growth improved in the latest week to its highest since August 2011, while the annualized growth rate also accelerated, a research group said on Friday.

The Economic Cycle Research Institute, a New York-based  independent forecasting group, said its Weekly Leading Index rose to 128.3 in the week ended Dec. 21 from 127.2 the previous week.

The index's annualized growth rate rose to 5.4 percent from 4.6 percent a week earlier. This was its best showing since late October.