Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Chinese travel agency Ctrip.com (Nasdaq: CTRP) dropped more than 13%, on four times the typical day's trading volume. The company has not publicly released news that would explain the large move in shares, but the company's stock is richly valued and tends to be volatile.

So what: Ctrip.com wasn't the only stock in its sector to trade down today. Shares of Expedia (Nasdaq: EXPE) and priceline.com (Nasdaq: PCLN) were both down more than 2% for the day while the S&P and Nasdaq were essentially flat, suggesting investor concern about the sector. The International Air Transport Association (IATA) released its latest outlook on the industry today, and despite a strong Q3, it's still forecasting a "pausing" in the recovery in 2011.

Now what: Prior to today's plunge, Ctrip shares were up more than 22% year to date, and the company was recently added to the Nasdaq 100. However, the company's shares are down more than 25% since the beginning of November. Watch for the stock to make more big moves based on the outlook for the global economy and air travel.

Interested in more info on Ctrip? Add it to your watchlist.

Fool contributor April Taylor does not own shares of the companies mentioned. priceline.com is a Motley Fool Stock Advisor selection. Ctrip.com International is a Motley Fool Hidden Gems recommendation. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.