(Dow Jones) A closely watched index of stock market volatility is starting to be used, at least experimentally, as a tool to value some assets for tax purposes. And recent moves in that index could yield gift and estate tax refunds for some wealthy people.

At least one appraisal firm is using the Chicago Board Options Exchange Volatility Index, or VIX, as a measure to value a private company stake or a large block of restricted public stock. It plans to use some of these valuations to apply for refunds on taxes paid for 2008 and 2009.

The firm, FMV Opinions, sees the VIX as a way to determine how much of a discount can be taken for tax purposes by the owner of an illiquid asset, such as a noncontrolling stake in a private company. The more volatile financial markets are, the more likely it is that the asset might have to be discounted to find a buyer.

The VIX has risen markedly as stocks have become more volatile in recent weeks, making it a good time to set the tax value of assets.

Lance S. Hall, cofounder and president of FMV Opinions, says his firm started developing the VIX as a tool to figure discounts after the market meltdown that began in Sept. 2008. He believes it can be used, along with restricted stock data found in Securities and Exchange Commission Forms 10-K and S-2, to show that valuations set in 2008 and 2009 were, in retrospect, too high. Clients can then use that information to file for refunds of overpayments.

Appraisers have not yet embraced the practice widely, but even those who don't see the VIX as a tool to value specific assets say the index has taken on more significance for them. It wasn't a focus before the recession, but has now "gotten the attention of more people across the financial markets," said Scott A. Nammacher, managing director, Empire Valuation Consultants, LLC.

The VIX become a new "general market risk" gauge to help people "better judge the size of these discounts relative to what is typically used in more stable markets," Nammacher said. He stressed that is still up to the appraiser to justify the discounts with specific models, studies or logic.

In estate and gift tax parlance, a stake in a company is known as a "fractional interest." A common estate planning technique for a wealthy business owner is to reduce the value of his company for tax purposes by giving gifts of minority interests to family. These gifted interests can be valued at a discount for gift tax purposes. Over time, a series of such gifts can remove the owner's "control" over the assets, allowing his remaining ownership to be discounted for estate tax purposes.

Even in the case of publicly traded company shares, discounts also apply if a taxpayer can prove to the Internal Revenue Service that shares of a public company are less marketable, usually because of contractual or regulatory restrictions-for example, in the case of an insider.

For many years, the tax authorities have accepted the use of restricted stock comparisons to determine discounts.