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 credit insurer Radian Group (NYSE: RDN) won't help pay your mortgage today; the share price has tanked to the tune of 12% today on above-average trading volume.

So what: Fellow mortgage insurance providers MGIC Investment (NYSE: MTG) and PMI Group (NYSE: PMI) also crashed hard today. MGIC sparked the slide by reporting a wider first-quarter loss than expected.

Now what: MGIC's troubles spell bad news for the entire mortgage insurance industry, because the terrible results stem from a sudden rise in claim payouts. A rising tide lifts all boats, but a bone-dry riverbed also leaves everybody equally stranded. Nearly 14% of MGIC's insured mortgage loans are currently delinquent.

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