New York ? A closely watched gauge of future economic activity rose a stronger-than-expected 0.5 percent in May, suggesting that the U.S. economy will continue sturdy expansion through the summer.

The Conference Board said Thursday its Composite Index of Leading Economic Indicators increased to 116.5 last month following rises of 0.1 percent in April and 0.8 percent in March. Analysts had been expecting an increase of 0.4 percent in May.

Ken Goldstein, economist for the Conference Board, noted that the index had risen in 13 of the past 14 months. The latest numbers, he added, “reflect a robust economic environment this spring and point to more of the same this summer.”

But Goldstein also cautioned that inflationary factors appeared to be building, which could encourage the Federal Reserve to raise interest rates sooner or faster to hold down price increases and cool the economy. At the same time, he added, business investment, inventory building and export growth looked solid.

“This confluence of economic strengths is a recipe for continued job gains, and possibly a little more inflation,” he said.

The index is closely watched because it is helps predict the economy’s path in the next six months.