All but four Iowa-based stocks that the Business Record follows gained ground in May.

Double-digit one-month gainers were Renewable Energy Group Inc. at 38.37 percent, KemPharm Inc. at 20.39 percent, American Equity Investment Life Holding at 17.35 percent, Workiva Inc. at 15.56 percent, NewLink Genetics Corp. at 15.35 percent and HNI Corp. at 11.14 percent.

The Iowa Index, an unweighted average price of 22 Iowa-based public companies, gained 3.47 percent. The Dow Jones industrial average gained 1.05 percent, the Nasdaq 5.32 percent.

Renewable Energy Group Inc. was the biggest gainer in the rolling one-year gains, up 57.96 percent from May 2017. Winnebago Industries Inc. was up 47.96 percent in the same period.

It should be noted that Windstream Holdings Inc. completed its previously announced 1-for-5 reverse stock split on May 25, decreasing the total number of shares outstanding from about 200 million to about 40 million.

The Iowa-based companies that make up the Iowa Index are in bold in this list of companies with sizable operations in the state.

See the full Iowa Index.