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 U.S. mortgage insurers took a beating today after MGIC Investment (NYSE: MTG) posted disappointing earnings. MGIC lost as much as 19% while Radian Group (NYSE: RDN) fell 15% and PMI Group (NYSE: PMI) slid 16%.

So what: There was definitely improvement in MGIC's results. For all of 2010, the company reported a $364 million loss as compared to a $1.3 billion loss in 2009. But that didn't help the fact that fourth-quarter results badly missed analysts' expectations. The company reported a $0.93 loss per share for the quarter on $361 million in revenue, versus analysts' estimates of a $0.61-per-share loss and $369 million in revenue.

Now what: The fourth-quarter results may not have even been what rustled investors' feathers. Looking ahead, MGIC's CEO said that claims in 2011 will likely be at or above the fourth quarter run rate. As for getting back to profitability? The company said: "[we] expect to continue to report annual net losses, and cannot assure you when we will return to profitability." Ouch!

Investors in Radian and PMI Group obviously took MGIC's earnings as a sign of things to come when those companies reveal their results next month. However, while it certainly doesn't say good things for the mortgage insurance industry, it's not necessarily a given that all of the companies are facing exactly the same problems. Radian is slated to announce its results Feb. 21, while PMI reports Feb. 16.

Want to keep up to date on these companies? Add MGIC Investment to your watchlist. Add Radian Group to your watchlist. Add PMI Group to your watchlist.

                

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.