Methods

This article is a reference section to verify that this package calculates various metrics correctly.

calc_iaao_stats

Coefficient of Dispersion (COD)

\[100 * \frac{\sum_{i=1}^N(SalesRatio_i - SalesRatio_{Median})}{N * SalesRatio_{Median}}\]

Price-Related Differential (PRD)

\[\frac{\frac{\sum_{n=1}^NSalesRatio_i}{N}} {\frac{\sum_{n=1}^N(SalesRatio_i*SalePrice_i)}{N}}\]

Coefficient of Price-Related Bias (PRB)

Arms-Length Measure

\[Percentile_{25}(SalesRatio) - (1.5 * IQR(SalesRatio)) < SalesRatio_i < Percentile_{75}(SalesRatio) + (1.5 * IQR(SalesRatio)) \]

regression_tests (from Hodge 2017)

Paglin

\[ AssessedValue = \alpha_0 + \alpha_1SalesPrice + \epsilon \]

Cheng

\[ ln(AssessedValue) = \alpha_0 + \alpha_1ln(SalesPrice) + \epsilon \]

IAAO

\[ AssessedRatio = \alpha_0 + \alpha_1SalesPrice + \epsilon \]

Kochin

\[ ln(SalesPrice) = \alpha_0 + \alpha_1ln(Assessed Value) + \epsilon \]

Bell

\[ AssessedValue = \alpha_0 + \alpha_1SP + \alpha_2SP^2 + \epsilon\]

Sunderman

\[ AssessedValue = \alpha_{00} + \alpha_{10}SalesPrice + \alpha_{01}Low + \alpha_{02}High + \alpha_{11}LowSalesPrice + \alpha_{12}HighSalesPrice + \epsilon \]