A measure of future U.S. economic growth picked up last week but the annualized growth rate slipped, 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 131.3 in the week ended Aug. 23, its highest in three weeks. It stood at 131.0 the previous week, a revision to the initially reported level of 131.1.

The index's annualized growth rate slipped to 4.2 percent, the lowest since the week ended July 19. It stood at 4.5 percent a week earlier.