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Estimates of home values from Zillow.com may be no more accurate than homeowners’ estimates of value, according to a new study in The Appraisal Journal’s Winter 2010 issue.

“Zillow’s Estimates of Single-Family Housing Values,” by Daniel R. Hollas, Ph.D., Ronald C. Rutherford, Ph.D., and Thomas A. Thomson, Ph.D., examines how Zillow’s estimates of value, known as Zestimates, compare to actual sale prices. Zillow.com is an automated valuation model Web site.

The authors looked at home sales in Arlington, Texas, a location where Zillow has indicated its data has the highest accuracy level. The authors’ study found that 40 percent of the homes in the sample were overvalued by Zillow by more than 10 percent compared to actual sale prices. The study’s authors suggested that Zillow may not take into account the occupancy of properties, which has been shown to affect sale prices. (The materials presented in the publication represent the opinions and views of the authors.)

Other studies have shown that on average homeowners’ overestimate the values of their homes by 5.1 percent and new owners overvalue their homes by about 8.4 percent. The authors conclude, therefore, that while Zillow is a helpful tool, it may not be more accurate than the owners’ own estimates of value.