Property Tax Fairness
From the Center for Municipal Finance

For Transparency & Equity in Property Assessments, we have developed a R package. This package analyzes the accuracy of property assessments and produces graphs, tables, and reports designed for general use. This package is produced by the Center for Municipal Finance, a research institute at the Harris School of Public Policy, University of Chicago.

For R code replication, please follow the below steps:

Install the package and load it.

# install.packages("devtools")

To conduct our study, we need data where every roll is a unique property’s sale price and assessed value for a given year.

#> 1 17273100931118      2015      53000          33860
#> 2 18013090421010      2018      80000          60390
#> 3 12111190201042      2018     118000         108300
#> 4 13093160601015      2017     125500          87200
#> 5 14322110150000      2018    3705000        3670740
#> 6 27021200080000      2016     345000         267280

Then, preprocess your data with reformat_data and call make_report. The report from the example below can be found here.

df <- cmfproperty::example_data

ratios <-
    sale_col = "SALE_PRICE",
    assessment_col = "ASSESSED_VALUE",
    sale_year_col = "SALE_YEAR",

                         jurisdiction_name = "Cook County, Illinois",
                         output_dir = "~/../Documents/GitHub/")

#output_dir is the directory in which report is saved; default is working directory

For a more replications and detailed guide on how to use this package, check out our Get started page.

This page contains instructions for users to generate reports by themselves. We provide the public datasets that users can download, and related source codes of R programs that users can run to generate Property Tax analysis reports.

Please click the desired counties (cities) below for the data and source codes. 

                  Code with Cleaned Data

                  Code with Raw Data

Our example_data has 4 variables: PIN, SALE_YEAR, SALE_PRICE, ASSESSED_VALUE. There are many variables in our dataset and in county reports, below are some most frequently appeared variables. The others can be found in the respective report and here.

Sales Ratio: The relationship between assessments and sale prices is regressive if less valuable homes are assessed at higher rates (relative to the value of the home) than more valuable homes.

CDO: Coefficient of Dispersion. The COD is a measure of assessment uniformity, or horizontal equity. It is the average absolute percentage difference from the median sales ratio.

PRD: Price-Related Differential. The PRD is a measure of regressivity, or vertical equity. A PRD of 1 indicates that homes are assessed at the same rate regardless of their sale price. A PRD greater than 1 indicates that less expensive homes are assessed at higher rates than more expensive homes, while a PRD less than 1 represents the opposite situation.

PRB: Coefficient of Price-Related Bias. The PRB is another quantitative measure of regressivity (vertical equity) which is an alternative to the PRD. PRB is a measure of how much assessed values change as a property’s market value increases.