Calculate sales ratio statistics using CCAO SOPs

Calculate sales ratio statistics (COD, PRD, PRB) according to Cook County Assessor's Office Standard Operating Procedures (SOPs).

The main SOPs affecting these calculations are:

Outlier trimming. Sales ratio performance statistics are quite sensitive to outliers. As a result, the top and bottom 5\ always dropped.
Minimum sample size. Sales ratio performance statistics can be inaccurate or misleading when the input sample is small. As a result, samples with less than 20 observations after trimming outliers will stop execution or will return NA if suppress = TRUE.

For more information on how each statistic or its confidence interval is calculated. See its respective function in the AssessR package.

ccao_cod(ratio, suppress = FALSE, na.rm = FALSE)

ccao_prd(assessed, sale_price, suppress = FALSE, na.rm = FALSE)

ccao_prb(assessed, sale_price, suppress = FALSE, na.rm = FALSE)

Arguments

ratio: A numeric vector of ratios centered around 1, where the numerator of the ratio is the estimated fair market value and the denominator is the actual sale price. NOTE: CCAO typically uses lagged or leading ratios to lessen the effect of sales chasing.
suppress: Default FALSE. A boolean value indicating whether or not to ignore minimum sample size requirements (N must be >= 20). If TRUE when N < 20, will return NAs.
na.rm: Default FALSE. A boolean value indicating whether or not to remove NA values. If missing values are present but not removed the function will output NA.
assessed: A numeric vector of assessed values. Must be the same length as sale_price.
sale_price: A numeric vector of sale prices. Must be the same length as assessed.

Value

A named list containing the statistic, its 95% confidence interval, whether or not the statistic meets the IAAO standard, whether or not the 95% confidence interval overlaps the IAAO standard, and the number of observations used to calculate the statistic (after outliers are removed).

Functions

ccao_cod(): Return named list of CCAO SOP compliant COD statistics.
ccao_prd(): Return named list of CCAO SOP compliant PRD statistics.
ccao_prb(): Return named list of CCAO SOP compliant PRB statistics.

Examples


# Load sample data from assessr
df <- assessr::ratios_sample

# Calculate performance stats using CCAO SOP defaults
ccao_cod(df$ratio)
#> $COD
#> [1] 12.12839
#> 
#> $COD_CI
#>     2.5%    97.5% 
#> 11.42146 12.88266 
#> 
#> $COD_MET
#> [1] TRUE
#> 
#> $COD_CI_MET
#> [1] TRUE
#> 
#> $COD_N
#> [1] 881
#> 
ccao_prd(df$assessed, df$sale_price)
#> $PRD
#> [1] 1.019631
#> 
#> $PRD_CI
#>     2.5%    97.5% 
#> 1.010899 1.028888 
#> 
#> $PRD_MET
#> [1] TRUE
#> 
#> $PRD_CI_MET
#> [1] TRUE
#> 
#> $PRD_N
#> [1] 881
#> 
ccao_prb(df$assessed, df$sale_price)
#> $PRB
#> [1] -5.926613e-05
#> 
#> $PRB_CI
#>       2.5 %      97.5 % 
#> -0.01013172  0.01001319 
#> 
#> $PRB_MET
#> [1] TRUE
#> 
#> $PRB_CI_MET
#> [1] TRUE
#> 
#> $PRB_N
#> [1] 881
#>