Stocks ended mostly lower on Wall Street, giving up a modest gain from earlier in the day after Fed Chair Janet Yellen gave an upbeat assessment of the economy, the AP reports. Yellen, speaking at a conference in Wyoming on Friday, said the case for raising interest rates has strengthened given improvements in the economy. Phone companies and utilities, which would suffer if interest rates rose and investors looked elsewhere for income, fell more than the rest of the market. The Dow Jones industrial average fell 53 points, or 0.3%, to 18,395. The Standard & Poor's 500 index slipped 3 points, or 0.2%, to 2,169. The Nasdaq edged up 6 points, or 0.1%, to 5,218.