Low oil prices combined with less demand around the world have weakened American stock prices. By the close of trading last week, the Standard and Poor's 500 was down more than 6 percent this year. But the S&P 500 Index rose 2.8 percent on Friday to rebound from a New Year's slump. On Monday, the S&P 500 was up 27 points to close at 1,945. The Dow Jones Average, the main measure of major American stocks, rose 228 points to close at 16,620. Wall Street traders and analysts are looking at factors that would keep the market in the positive. But for now, Wall Street watchers expect extreme ups and downs. The term “choppy trade” is used often now on Wall Street. A choppy market occurs when prices swing up and down with no major price movement in either direction.