CHICAGO – A Nobel Prize-winning University of Chicago economist whose work on the economics of slavery triggered a furious national debate has died.

The university says in a statement that Robert Fogel died Tuesday after a brief illness. He was 86.

Fogel wrote 22 books, the last one published in April. He first came to prominence in academic circles in the 1960s when he concluded that railroads weren't as important to the nation's economy as was widely believed.

In the 1970s, he and co-author Stanley Engerman challenged the long-accepted assumption that slavery was inefficient and unprofitable with "Time on the Cross: The Economics of American Negro Slavery."

The Royal Swedish Academy of Sciences cited both his work on railroads and slavery when it awarded him the 1993 Nobel Prize for Economics.

WASHINGTON – Chief executives for the largest U.S. companies are more optimistic about sales over the next six months and plan to add more workers.

The Business Roundtable said Wednesday that its April-June quarterly survey found 32 percent of its members expect to expand payrolls in the next six months. That's up from 29 percent in the January-March survey. And 78 percent expect their sales to increase. That's up from 72 percent from the previous survey.

Consumers have kept spending this year, despite an increase in Social Security taxes.