OMAHA — A monthly economic index for nine Midwestern and Plains states has inched up to hit another three-year high, suggesting more economic growth over the next three to six months.

A report issued Monday says the overall Mid-America Business Conditions Index rose to 60.5 in May from 60.4 in April, which also was a three-year high.

Looking six months ahead, the business confidence portion of the overall index dropped to 62.5 from 64.2 in April.

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

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