A new computer system could be in order for two county assessors if an upcoming bill passes in the Utah Legislature.

During 2007, residents in Bountiful were hit by double-digit property tax increases because their property hadn't been re-appraised in 10 years.

Once their property values were adjusted to an accurate market value, property taxes went up, as well.

HB54, sponsored by Rep. Wayne Harper, R-West Jordan, aims to fix that by requiring assessors of Utah's 10 most populous counties — those of 31,000 residents or more — to use a computer-assisted mass-appraisal system to conduct their annual update of property values.

Most of those counties — Salt Lake, Utah, Davis, Weber, Washington, Box Elder, Iron and Summit — already have such systems in place. Only Cache and Tooele counties don't but would have until Jan. 1, 2011, to begin using appraisal software.

Summit County recently purchased such software for its assessor's office for $92,000.

The bill also requires those counties to maintain a record of the last appraisal date for each parcel of real property in the county on the county's computer system and to include the last appraisal date for a parcel of property on the property owner's tax notice, as well.

Counties already maintain appraisal dates, and adding the date for the most recent appraisal to a tax notice or valuation notice wouldn't be complicated, said Davis County Assessor James Ivie.

But using a computer-assisted appraisal system that employs multiple-regression analysis doesn't make much sense if you don't have accurate data, assessors argue.

In some neighborhoods in Washington County where homes don't sell rapidly, says assessor Art Partridge, he doesn't get much sales data he can use to judge market value of those homes.

Regression analysis requires a large sample of data, and when you don't get the data, you don't get accurate results.

"Garbage in, garbage out," assessors are fond of saying.

A similar problem is evident in appraising commercial properties, which don't change hands as often as residential properties, though some commercial properties in Salt Lake County are valued in an automated fashion.

Utah County is moving in that direction, Assessor Kris Poulson said.

In most cases, though, it takes old-fashioned legwork to visit commercial properties to make sure values are accurate.

Partridge said Harper's bill would be better served by a companion bill to make Utah a disclosure state — one that requires a property's sale price to be recorded on the deed filed with the county.