DES MOINES, Iowa (AP) ¿ Shares of exchange and trading platform providers mostly fell Friday as the broader markets trended downward and an analyst downgraded or lowered estimates on several companies. GFI Group Inc. fell 54 cents, or 7 percent, to $7.15 after Keefe, Bruyette & Woods analyst Niamh Alexander downgraded the inter-dealer broker, which specializes in derivatives and related products. The analyst cut the stock to "Market Perform" from "Outperform" saying there's more upside potential in other stocks in the sector that are better prepared in a changing derivatives trading landscape. Alexander said proposed legislation could force changes in over-the-counter trading could result in lighter volumes for the company. Other exchange stocks that fell in midday trading included Nasdaq OMX Group Inc., down 56 cents, or 2.7 percent, to $19.85; NYSE Euronext, down 54 cents to $29.40; and Interactive Brokers Group, which fell 72 cents, or 3.4 percent, to $20.21. Alexander downgraded Nasdaq to "Market Perform" from "Outperform" and lowered his 2010 earnings estimate to $2.12 from $2.32. He concluded the business mix, market position and extent of cost cutting leaves the company with "fewer positive catalysts ahead and room for more downside risk to estimates."