The market has been slipping so far today: the Nasdaq is trading down 1%; the S&P 500 is down 0.6%; and the Dow has slipped 0.8%. The Nasdaq Composite Index represents all the stocks that trade on the Nasdaq stock market.

The biggest movers traded on the NASDAQ so far are:

Company Market Cap Percentage Change
Penn National Gaming (Nasdaq:PENN) $2.88 billion +28.7%
Sears (Nasdaq:SHLD) $6.23 billion -17.5%
SINA Corporation (Nasdaq:SINA) $3.53 billion -15%
Ameristar Casinos (Nasdaq:ASCA) $552.8 million +13.2%
MTS (Nasdaq:MTSC) $789.5 million -10.7%
Cyberonics (Nasdaq:CYBX) $1.29 billion +8.6%
Regeneron Pharmaceuticals (Nasdaq:REGN) $13.76 billion +7.5%

Broker Summary: E-Trade Financial

Penn National Gaming (Nasdaq:PENN) is currently at $48.41 per share after a dramatic increase of 28.7%. At 7.2 million shares, the company's volume so far today is above yesterday's volume of 632,179 shares.

Taking a 17.5% hit, Sears (Nasdaq:SHLD) is currently trading at $48.22 per share. This morning, the company is trading a volume of 3.8 million shares. This is five times the current three-month average.

SINA Corporation (Nasdaq:SINA) is currently trading at $45.11 per share, after a steep drop of 15%. The company is currently trading a volume of 5.7 million shares.

After a big jump of 13.2%, Ameristar Casinos (Nasdaq:ASCA) is trading at $19.08 per share. So far today, the company's volume is two million shares, 12.6 times the average daily volume.

MTS (Nasdaq:MTSC) is at a share price of $43.76 after a sharp decline of 10.7%. The company is trading at a volume of 116,127 shares. This is more trading activity than there was yesterday.

Cyberonics (Nasdaq:CYBX) has increased to a share price of $50.60, a 8.6% rise. With 416,546 shares changing hands so far today, the company's volume is 1.8 times its current three-month average.

Regeneron Pharmaceuticals (Nasdaq:REGN) is at $153.12 per share after an increase of 7.5%. The company's volume for the day so far is 579,910 shares.

The Bottom Line No matter the economic climate, Wall Street will always have stocks that make major moves each week. It is important to weigh current activity against historical performance when making any investment decisions. Keep in mind that all these ratios should be compared against historical numbers and industry information in order to get a more complete picture.