An independent study to gauge the fairness and accuracy of residential property tax assessments in Cook County was scheduled to be completed in mid-December, records show, but now its first findings may not be delivered until the end of February — days after early voting commences in an election that could be affected by the results.

The study was ordered nearly seven months ago by Cook County Board President Toni Preckwinkle after the Chicago Tribune published the first three parts of “The Tax Divide,” an investigation that found high error rates in residential property valuations produced under Assessor Joseph Berrios. The assessments also burdened poorer homeowners with unfairly high tax bills while giving wealthier taxpayers a break.

Planning documents from August show that the independent study is based on the same kind of statistical analysis carried out by the Tribune with the goal of determining whether assessments under Berrios have met standards used in municipalities around the world.

Several of the country’s leading experts in assessments said that kind of study should take no longer than one or two months. Yet the results are now not expected to come out until a few weeks before the March 20 primary. Early voting starts Feb. 21 in downtown Chicago and four suburban locations, and in most suburbs on March 5.

“The more time you have to do a study, the more (issues) you can look at and the more careful you can be,” said Richard Almy, a former executive director of the International Association of Assessing Officers. “But the analysis can be done in a couple of months if you have all the data.”

A fourth “Tax Divide” story, which documented problems with assessments of commercial and industrial property, was published by ProPublica Illinois and the Tribune in December, adding to intense scrutiny of Berrios as he fights for re-election in a contested primary. His opponents — asset manager Fritz Kaegi and property tax consultant Andrea Raila — each have cited the reporting on the campaign trail and pledged to fix the problems it identified.

County Commissioner Jesus “Chuy” Garcia, who backs Kaegi, said “the voters deserve some answers” about the fairness of the assessment system. He backed the idea of doing the study but said he now believes “that was probably all a delay tactic.”

“Some of us have a lot of doubt about whether this was a real, credible undertaking or not — so prove us wrong,” Garcia added.

Preckwinkle’s spokesman, Frank Shuftan, said Monday that the study is on schedule.

“This is a big project that takes time, given the size and number of residential properties in Cook County,” Shuftan said. “The first phase was information-gathering, which was completed by mid-December. The analysis of the data is nearing completion and the consultant’s measurement of the office’s performance, based on the analysis, will be announced prior to the end of February.”

But in August, at a planning meeting for the study, the independent group overseeing the effort handed out a document that laid out a different schedule. The document, provided to a reporter by Cook County Clerk David Orr, shows that “specific improvement areas” were to be identified before Thanksgiving and work on solutions was to be completed by mid-December.

The pro bono study is being led by the Civic Consulting Alliance, or CCA, a nonprofit consulting firm that has provided technical assistance for several Chicago mayors, as well as for Preckwinkle. The group operates under the umbrella of the Civic Committee of the Commercial Club of Chicago, a nonprofit good-government group consisting of chief executives from the region’s largest employers.

Preckwinkle and Berrios have been mum on what is being learned through the study process, with Preckwinkle saying she’s not at liberty to talk about it. “All I can tell you is that there’s a confidentiality agreement between the assessor and CCA about the work,” Preckwinkle said in a recent interview.

Orr, who also is supporting Kaegi, called on the CCA to release the study’s results immediately.

“The CCA is a credible organization, but they are unfortunately gaining the reputation of helping with what has become a big stall until after the March 20th primary election,” Orr said.

A spokeswoman for the CCA and the Civic Committee declined to comment, referring questions about the study to the assessor’s office.

Berrios spokesman Tom Shaer said “the assessor’s office plays no role in the timing or schedule of CCA’s work” and that anyone speculating on how long the study would take doesn’t understand the scope of the undertaking.

“Mid-December may have been part of CCA’s initial thoughts before it began the extensive information-gathering and other work required,” Shaer said.

The issue of unfair property tax assessments is hanging over the re-election campaigns of both Preckwinkle and Berrios, who are friends and allies. Berrios is chairman of the Cook County Democratic Party, Preckwinkle is vice chairman, and the pair filed their re-election paperwork together as part of an endorsed slate of candidates.

The relationship between the two has caused critics of the assessor’s office to question whether the study is aimed at providing political cover for Berrios. Preckwinkle announced the study at a County Board hearing in July where commissioners questioned Berrios over “The Tax Divide” — a move that took some of the heat off of her ally.

At a meeting of the Tribune Editorial Board last week, Preckwinkle declined to criticize Berrios’ performance. “I’ve worked closely with Joe Berrios in areas where I think he’s done good work,” she said.

Berrios has steadfastly contended that his office produces fair and accurate assessments. The assessor disputed findings from the investigation, saying the analyses were not conducted by assessment professionals. The Tribune and ProPublica Illinois vetted their methods with top experts in the field.

Preckwinkle has said the aim of the CCA study is not to protect Berrios but to conduct a thorough review of the entire property tax system.

The CCA study will look only at residential assessments, however, leaving unexamined the fairness and accuracy of commercial and industrial assessments, which make up roughly a third of the county’s property tax base.

Numerous independent studies, including by the University of Chicago and the Illinois Department of Revenue, already have found assessments to be deeply flawed.

“We don’t need another study to tell us the system stinks,” said University of Chicago public policy professor Christopher Berry, who studied the system while developing a new residential valuation model for the county that was never implemented. “If Toni Preckwinkle doesn’t believe the studies already done by the University of Chicago, the University of Illinois, the Illinois Department of Revenue and the Tribune, then she is simply choosing not to see the truth right in front of her face. She is siding with Joe Berrios over the truth, and over her constituents.”

Berry, along with a Tribune reporter, also led a graduate-level class at U. of C.’s Harris School of Public Policy that examined the county’s residential appeal system. The study, which was featured in “The Tax Divide,” found the process made assessments more unfair. The assessor’s office dismissed the findings of that study as well as Berry’s criticisms.

The planning documents from August show the CCA study is using performance measures set by the International Association of Assessing Officers, which involve comparing the assessor’s estimated market values to actual sales data. Two of the most important statistics are the coefficient of dispersion, essentially a rate of error, and the price-related differential, a measure of fairness.

The Tribune’s analysis found that the office violated industry standards for both measures for years, sometimes by a large margin. Highly inaccurate assessments wound up handing unsanctioned property tax breaks to well-off homeowners while punishing those who have the least, particularly people living in minority communities.

Peter Davis, an assessing expert who specializes in sales ratio studies, said that once the data is in hand, a ratio study should take no more than a month.

In mid-January, a County Board committee scheduled a hearing to get an update on the progress of the study. Berrios, however, did not show up; his office cited a prior engagement. No new meeting has been set.

That prompted concerns that the study wouldn’t be made public before voters go to the polls for the primary.

“I think Mr. Berrios and Madam President Preckwinkle are going to do everything they can to keep him from appearing before the board between now and March 20 to talk about the study,” said Commissioner Richard Boykin, an Oak Park Democrat who represents large swaths of Chicago’s West Side and suburban Maywood, two areas where many low-income African-American homeowners live.

“We already know what the results are,” he added. “We already know that there’s a problem and quite frankly, we already know that there needs to be a solution articulated for the voters before March 20.”

With pressure mounting, Preckwinkle spokesman Shuftan crafted a response on letterhead from Berrios’ office last week stating that some of the results were expected by the end of February. What specifically will be released is unclear, however.

Amid calls to release the study, some observers who have studied the system are convinced the exercise is unnecessary.

“What could the study possibly show that would make any difference?” said Berry, the U. of C. professor. “If it says the system is broken, then it’s just confirming what we already knew and we’re right back where we were in July. If it says the system is working, then it will contradict every expert who has come before, and everyone will know that the new study is bogus.”