OMAHA, Neb. — A monthly economic survey index for nine Midwestern and Plains states has slumped after hitting a three-year high a month earlier.

A report issued Friday says the overall Mid-America Business Conditions Index dropped more than 3½ percentage points in July, to 57.0. The index had risen slightly in June, to 60.6.

Looking six months ahead, the business confidence portion of the overall index also declined. It hit 60.0 last month, compared with 63.6 in June.

The survey results from supply managers are compiled into a collection of indexes ranging from zero to 100. Survey organizers at Creighton University say any score above 50 suggests economic growth, while a score below that suggests decline.

The survey covers Arkansas, Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, Oklahoma and South Dakota.