U.S. services firms expanded at a faster pace in November, a signal that overall economic growth should remain robust.

The Institute for Supply Management says its services index rose to 59.3 last month, up from 57.1 in October. The index reached 59.6 in August, the highest in eight years. Any reading over 50 indicates expansion.

The ISM is a trade group of purchasing managers. Its survey of services firms covers businesses that employ 90 percent of the American workforce, including retail, construction, healthcare and financial services firms.