As a Democrat from Baltimore County, Md., Jon Cardin didn’t fit the profile of a state delegate who would vote against in-state tuition for undocumented immigrants. But an eye-popping fiscal note from state legislative analysts convinced him that the bill -- a popular liberal reform measure -- would be unfeasible.

While Maryland lawmakers were debating the bill in 2011, the state Department of Legislative Services predicted that enrollment by undocumented immigrant students would ratchet up annual higher education costs -- with no new revenue -- by more than $3.5 million in 2016.

“If we could figure out a way to make it budget neutral, I would not only vote for it, I would be the No. 1 cheerleader,” Cardin said. Instead he abstained when it passed out of the Ways and Means committee, voted no on a preliminary version and abstained again in the final House vote.

Cardin heard from progressive advocates -- normally his political allies -- and even from his own wife saying they were disappointed in him. Cardin even had personal reasons to support the bill: His Jewish great-grandparents experienced discrimination when they immigrated to the United States from Eastern Europe decades ago. But while Cardin whole-heartedly supported the bill on principle, he couldn't justify its projected costs. (Maryland voters ultimately approved the new law in a November 2012 referendum.)

As Cardin's experience shows, projected costs can be a major factor in considering legislation to offer in-state tuition to undocumented immigrants, also known as "tuition equity" bills. The price tag of tuition equity bills can kill their chances of becoming law. When Maryland’s General Assembly passed a tuition equity bill in 2003, Gov. Robert Ehrlich vetoed it because he said the fiscal cost to the state was impossible to know and could be too large.

Such measures have been introduced in more than a dozen states this year. Depending on the number of students who take advantage of the tuition, the bills can be cast as either fiscal drains or financial boons.

But when it comes to predicting how many new students actually will enroll, well, no one can be sure.

“The projections are a non-exact science,” said Oregon Rep. Mark Johnson, a Republican who supported a tuition equity bill in a House committee vote in February. “It’s really hard to predict accurately.”

The methodology for forecasting the fiscal impact of tuition equity bills varies significantly from state to state. In Maryland in 2011, the Department of Legislative Services assumed an extreme scenario: All undocumented immigrants eligible for the tuition would enroll exclusively in community colleges -- which is only required for the first two years. (That would be especially expensive to the state, because community colleges can't offset the new lower-paying enrollees with high-paying out-of-state students. The legislative department assumed those students would never transfer to four-year state universities, where higher enrollment might eventually mean at least some tuition revenue for the state.)

The Maryland Legislative Services department also assumed a relatively high number of undocumented immigrants would enroll: 366. To put that in perspective, California reported 634 potentially undocumented students took advantage of its in-state tuition law in the entirety of the University of California system in the 2010-2011 school year, after nine years of growing annual enrollment. (In 2002-2003, the first school year under the new law, California recorded 90 potentially undocumented students.)

Other states have made assumptions that tuition equity would be a fiscal benefit: In Oregon, the Legislative Fiscal Office estimated that just 38 students would take advantage of the lower tuition rate between 2013 and 2015. About 80 would enroll at the lower rate in the two subsequent years. Not only that, but the fiscal office said that the enrollees would generate about $1.9 million in revenues over the next four years without warranting new expenses for additional buildings or staff. The forecast assumed that undocumented immigrants who take advantage of the lower rates would be new students who couldn’t afford college prior to the policy change.

“I think that analysis helps Republicans support it,” said Sen. Chuck Thomsen, a Republican co-sponsor of Oregon’s tuition equity bill. Thomsen said he suspects the number of students who would enroll would be higher than what the legislative fiscal office projects. Nonetheless, the fact that the fiscal analysis shows low enrollment and a moderate boost in revenues “does soften the blow for Republicans,” he said.

For Rep. Kevin Priola, a Republican lawmaker in Colorado who supported a tuition equity bill in an appropriations committee vote this year, the imprecision of legislative forecasts doesn’t really matter. Fiscal notes are focused on the direct impact of legislation; they don't take into account the broader economic returns a state might see, he said. “I looked at it from a dynamic modeling perspective. We’ll have more productive citizens earning higher incomes, having a better impact on society and being less of a burden on social services.”

In Colorado, the legislative fiscal office concluded that up to 500 students would enroll in state universities in the next school year if legislators pass a tuition equity law, raising about $2 million in tuition revenue, but also costing the state some $930,000 in college assistance stipends. That calculation derived from existing administrative data on high school graduates who do not attend college, of which about 33 percent are thought to be undocumented immigrants and about 24 percent were Hispanic. Multiply those two percentages by the 16,920 high school graduates in 2011-2012 who didn’t attend college and the result is 1,511 undocumented immigrants who would qualify for in-state tuition. The office then lowered its estimate to reflect that not everyone who would qualify would actually attend college.

Colorado’s legislative analysts had good reason to assume that the eligible population would not reflect the number who actually attend college. Even with in-state rates, many undocumented immigrants would face barriers likely to keep them from attending college. When the Migration Policy Institute analyzed the potential impacts of the federal Development, Relief, and Education for Alien Minors (DREAM) Act legislation in 2010, it noted that many of the eligible beneficiaries came from low-income backgrounds and wouldn’t be able to afford in-state rates; undocumented immigrants who qualified were also likely to have either work or parenting conflicts with full-time class schedules.

“We’re expending so much political capital trying to get the DREAM act or these in-state tuition laws,” said Margie McHugh, co-director of the Migration Policy Institute’s National Center on Immigration Integration Policy. “Most of these people are low-income and are not academically prepared for college-level courses. We have every reason to believe that their uptake would be extremely low.”

Tanya Broder, a senior attorney at the National Immigration Law Center, gave at least one more reason why projections might be higher than the actual participation rate, at least initially: Young immigrants who would only attend with in-state tuition don’t know the law has changed. “It takes time for the message to get out,” she said.