Eight professors and economists, plus two of Ogden's staffers, examined the study. The volunteers were: Perlich; Eric Eide, associate professor of economics, Brigham Young University; Boyd Fjeldsted, private forensic economist; Patrick Galvin, associate professor at the U.'s College of Education; Lars J. Lefgren, assistant professor of economics at BYU; Mark Showalter, BYU associate professor of economics; Roger Tew, attorney, and former Utah State Tax commissioner and a consultant for the Utah League of Cities and Towns; and David Kiefer, U. economics professor.

The study's numbers hinge on two variables: how many people would switch to private schools under a tax credit and marginal costs, or the cost of adding the next student to — or taking her away from — the public school system.

Scenarios in an updated copy of the study show tax credits could cost the state $179.3 million at worst, or save up to $1.2 billion, depending on the variables. Basically, the more students who switch, the greater the savings. And most scenarios predict savings.

But the reviewers question the methodology.

The study actually found that the price elasticity, or the degree to which Utah residents would respond to private schools based on price, at practically zero, the reviewers pointed out. That's possibly because LDS Seminary handles most of the parochial school demand within the public system, Tew noted.

However, the study then goes on to use price elasticity of 0.5 to 2 — high, but within possibility in a state with so few students now in private schools, Herzberg said.

In Utah, about 3 percent of the school age population, versus some 13 percent nationwide, attend private schools.

"Utah is, in our sense, at a bit of a turning point in terms of population and diversity . . . that might lead to something closer to the national average," Herzberg said. "An estimation of 3,000 additional students is not a high estimation."

But study reviewers noted the national price elasticity is about 0.48, which would likely indicate little or no savings. Besides, added Perlich: "If diversity is driving more people to private schools, why do we need a tuition tax credit?"

The panel also questioned the study's use of a marginal cost, an economic model that figures in all costs of educating a child, including buildings, and all funding, including federal.

The marginal cost used is $8,675; Utah's often cited per-student spending figure is closer to $5,000.

"We know it's high, but it's what (the state has) been doing" in terms of total student spending, Herzberg said. "To look at just what the state . . . is (spending) would be to underestimate the impact of taking a child out of a school."

But the marginal cost is incompatible with state education funding, the reviewers said. And since the findings are to determine how the state funds public education, it should use state per-student spending dollars in the analysis.

Ogden will report the findings at a Utah State Board of Education meeting on Jan. 12.

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E-mail: jtcook@desnews.com