Top-tier homes make up almost twice the proportion of foreclosures as they did just three years ago, according to Zillow.com data, confirming the widespread perception that foreclosures are moving up-market.

Zillow divided the market into three tiers according to home values and found that in 2006, at the height of the real estate bubble, homes in the bottom one-third of home values made up almost 55 percent of all foreclosures.

Homes in the middle tier made up almost 29 percent of foreclosures and homes in the top tier represented only 16 percent.

Since then, there’s been a dramatic shift in the distribution of home values among foreclosed homes, Zillow said.

In July 2009, the bottom tier made up 35 percent of foreclosures, while the middle tier accounted for 35 percent, and the top tier for 30 percent.

Zillow says the shift to more foreclosures outside the subprime markets (and in higher priced segments of the market) results from high delinquency rates in prime, Alt-A, and Option ARM mortgage products and declining cure rates.

Zillow cited a recent study by Amherst Securities Group that showed higher delinquency rates for these products and the strong relationship between increased negative equity and decreased probability of resolving delinquency status.

As of the end of the second quarter of this year, Zillow estimated that 23 percent of single-family homes with mortgages are underwater, indicating that cure rates are likely to remain lower than they would be otherwise.

To avoid any distortions from variations in home prices across the nation in this analysis, Zillow compared home values to the median value in the local market and allotted them to tiers on that basis.