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 private mortgage insurer MGIC Investment (NYSE: MTG) jumped as much as 15.6% amid fairly heavy trading and a generous sprinkling of fairy dust.

So what: Real estate e-formation specialist Zillow (Nasdaq: Z) just published a study saying that the free-falling prices of American homes could start to bounce back in 2012. A survey of 109 economists places the rebound in early 2013 at the very latest.

Now what: Homebuilders are sitting out this jump because they got theirs earlier this week. Fellow PMI insurer Radian (NYSE: RDN), on the other hand, is enjoying a double-digit jump as well. This potential turnaround comes too late for largest PMI expert PMI Group, which filed for bankruptcy in November -- only the strongest businesses survive a multi-year market slump.

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