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Assessor’s Office new residential property assessment model unveiled for Tax Year 2018 reassessment
Early indicators of accuracy meet industry standards and criteria for minimal regression

Wednesday, May 02, 2018
Special to suffredin.org

Chicago - Cook County Assessor Joseph Berrios has announced that the first reassessment

of residential properties using a new assessment model has met the longstanding goal of

reducing regression. This creates more accurate assessed values of homes.

The system for residential property assessment in Cook County has been in existence for 40

years. Assessor Berrios inherited that system and its issues. He and his staff pledged to work

with the Civic Consulting Alliance (CCA) and Tyler Technologies to improve residential

assessment modeling and related processes. Work with Tyler actually began years ago.

“Improving residential assessment has been a priority during my time in office. It pleases me

tremendously to see we are achieving what we set out to do, and new resources now

available to us from CCA and Tyler have helped. This is a huge step forward for Cook County,”

Assessor Berrios said.

The Assessor added, “I thank County Board President Toni Preckwinkle for her help with the

Tyler Technologies contract, CCA for its important role, CCA expert Josh Myers, Tyleraffiliated

expert Dr. Richard Borst and Tyler for its overall fine work. Everyone in the

Assessor’s Office worked diligently to meet the goal of improving the assessment process.”

The Assessor’s Office triennially reassesses one-third of the more than 1.8 million parcels of

property located in Cook County. In this tax year (2018), the reassessment is of all properties

in the City of Chicago.

Rogers Park Township, one of the eight townships comprising the City, is the first township

whose reassessment notices have been mailed. Approximately 11,000 parcels of residential

real estate were reassessed there using the new model. Numerous indicators including

coefficient of dispersion (COD) are well within industry standards of the International

Association of Assessing Officers (IAAO).

This most recent work reflects interactive collaboration between the Assessor’s Office and

newly available, renowned valuation and modeling experts and researchers at CCA and Tyler.

Due to the sophistication of these state-of-the art improvements in techniques, the model

performance was superior. Results include:

 

? Both linear additive and multiplicative (a/k/a log-linear) model structures were evaluated

in light of IAAO standards

? COD, coefficient of variation (COV), price-related differential (PRD) and pricerelated

bias (PRB) are all well within IAAO standards.

? The multiplicative model structure was chosen because of its superior performance

measures.

? Outlier identification was based on statistically-founded and defensible methods

? Geostatistical methods were used to derive a location influence factor intended to

improve model performance. The location factor variable was significant and helped to

improve accuracy.

? The valuation procedure used the comparable sales direct market comparison method

of valuation.

? Performance measures of accuracy ultimately obtained were superior to traditional

modeling techniques

? There has been a significant reduction in the number of necessary hand checks

? Geospatial analytic methods were employed to ensure that there was no spatial bias in

the valuation model. Model performance demonstrated a lack of spatial clustering.

“We have never wavered from our commitment to reducing regression and assessing property

as accurately and fairly as possible,” said Assessor Berrios.

Reassessment notices contain proposed property values for Tax Year 2018, which will be

reflected on Second-Installment Tax Bills to be mailed and due in the summer of 2019. Each

“Assessed Value” is 10% of a home’s estimated market value.



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