Price-Related Differential (PRD)

assesspy.prd(assessed, sale_price)

PRD is the mean ratio divided by the mean ratio weighted by sale price. It is a measure of vertical equity in assessment. Vertical equity means that properties at different levels of the income distribution should be similarly assessed.

PRD centers slightly above 1 and has a generally accepted value of between 0.98 and 1.03, as defined in the IAAO Standard on Ratio Studies Section 9.2.7. Higher PRD values indicate regressivity in assessment.

Note

The IAAO recommends trimming outlier ratios before calculating PRD, as it is extremely sensitive to large outliers. PRD is being deprecated in favor of PRB, which is less sensitive to outliers and easier to interpret.

Parameters:

• assessed (numeric) – A numeric vector of assessed values. Must be the same length as sale_price.

• sale_price (numeric) – A numeric vector of sale prices. Must be the same length as assessed.

Returns:

A numeric vector containing the PRD of the input vectors.

Return type:

float

Example:

# Calculate PRD:
import assesspy as ap

ap.prd(ap.ratios_sample().assessed, ap.ratios_sample().sale_price)