Excerpt: Wal-Mart Stores Inc., the world's largest employer, asked nine economists to assess its effect on the economy. Today [November 4], at a conference organized by the company, they'll tell Wal-Mart that it's far from an exemplary employer. Wal-Mart causes wages to fall for workers in towns where it operates, depresses pay for unskilled laborers and increases Medicaid costs, according to economists who will present their findings at today's meeting in Washington.