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Credit scores are designed to predict the risk of default. If your scores are good, lenders see you as someone who is likely to keep paying your debts.

But when it comes to strategic default -- which is when people who can afford to pay their mortgages don't, usually because their homes are worth less than their loans -- analysts have noticed a reverse phenomenon: Good credit scores can indicate a higher likelihood a homeowner will voluntarily bail on a home loan.

Somewhere around one in three mortgage defaults these days is strategic. Those strategic defaulters, when compared with other people who stop paying their mortgages, are more likely to:

  • Have better previous credit histories.
  • Have lower account balances.
  • Stay under their credit limits (they're less likely to have maxed-out accounts).
  • Use less of their available limits.

"People who make the decision to strategically default tend to be more savvy," said Andrew Jennings, the chief analytics officer for Fair Isaac, the company that created the leading FICO credit score. "Most of the people who walk away from a mortgage are saying, 'This is not a contract that makes sense anymore.'"

Liz Weston

Liz Weston

FICO analysts looked at a population of borrowers who started out current on all their bills but wound up 90 days or more behind on their mortgages.

The people who stayed current on their other bills but stopped paying their mortgages had better initial FICOs and lower credit balances, and were less likely to have gone over their limits -- all signs of responsible money management.

They also:

  • Had been in their homes for shorter periods than other defaulters, a possible indication that they were less attached (emotionally or financially) to the properties.
  • Were more likely to have opened credit accounts in the previous six months -- perhaps in preparation for the periods after their defaults, when getting credit would be tough.

Intriguingly, one factor that wasn't a strong predictor of strategic default was how far "underwater" these homeowners were. What mattered far more was the future trajectory of home prices.

In other words, whether the borrowers owed a lot more than their homes were worth, or only a little more, wasn't as key to predicting strategic defaults as whether home prices were predicted to continue falling.

Another, perhaps surprising, point that didn't matter: whether the homeowners lived in states that allowed lenders to sue borrowers for unpaid mortgage balances. FICO's research indicated that 40% of strategic defaulters lived in "recourse" states, where they could face lawsuits over debts that remained after foreclosure. It's not clear whether defaulters didn't understand the risks or whether they had bet that their lenders wouldn't come after them.

FICO researchers examined credit files for over 3.2 million mortgage-holding homeowners, including about 50,000 they identified as strategic defaulters and 150,000 as non-strategic defaulters.

"While the answer is probably a little different for different people, our feeling is that people take this action without fully understanding the consequences," Jennings said. "The action is encouraged because there are any number of websites for companies that help people plan and execute a strategic default. The message coming from them is that if enough people take this action, there is no way the banks are going to come after us, and even if they do, you can declare bankruptcy."

FICO analysts teased out what's predictive of strategic default, and what's not, as a way to sell another product to lenders: a formula that could help them identify which of their loans are at risk despite the lack of other red flags, such as maxed-out credit cards and other skipped payments.

Lenders increasingly need this help, since strategic default dumps the traditional "payment hierarchy" on its head. In the past, lenders could count on people skipping other payments first before they reneged on their mortgages. Skipped payments caused credit scores to plunge, alerting mortgage servicers to the upcoming problem so they could intervene -- with counseling, workout proposals, threats of lawsuits and so on.

Fair Isaac is selling its new product as a way lenders can start tracking loans at high risk of strategic default and perhaps start intervention earlier.

There's likely to be a need, because the trend seems to be growing. A study at the University of Chicago's Booth School of Business found that 35% of mortgage defaults in the U.S. were strategic in September 2010, compared with 26% in March 2009.

If you're thinking about skipping out on your mortgage, here's what you need to keep in mind:

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  • The foreclosure process varies by state and by lender. Don't count on other people's experiences to predict your own. Attorney Stephen Elias' book "The Foreclosure Survival Guide" is a good primer in what you should expect and what your alternatives might be.
  • Your risk varies, too. Some states, including California, prohibit lenders from suing you for mortgage balances you owe on a primary residence if you used the loan to buy the property and didn't refinance. Many other states allow the lawsuits. Before you stop paying, talk to a bankruptcy attorney who is familiar with the credit and real-estate laws in your state as well as industry practices. You can get a referral from the National Association of Consumer Bankruptcy Attorneys.
  • Understand what a foreclosure does to your credit. The higher your credit scores, the longer they will take to heal. Read "Bounce back from bad credit" for details about how much a hit your scores can take and how you can rehabilitate your credit.

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.