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Merged
Damonamajor merged 2 commits into from
Sep 16, 2025
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Add comment for mki #20

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3468661
Update formulas.R
Damonamajor Sep 16, 2025
33d1bbc
Update formulas.R
Damonamajor Sep 16, 2025
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9 changes: 9 additions & 0 deletions R/formulas.R
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Expand Up @@ -178,6 +178,15 @@ prb <- function(assessed, sale_price, na.rm = FALSE) {
# Calculate the Gini cofficients needed for KI and MKI
calc_gini <- function(assessed, sale_price) {
df <- data.frame(av = assessed, sp = sale_price)
# This Gini coefficient algorithm is sensitive to the order of the input
# observations: If multiple observations share the same sale price but have
# different estimates, the output coefficients will be different depending
# on which of the sales with identical prices gets ordered first in the
# input dataframe. To ensure a stable sort order, Quintos recommends
# sorting by ascending sale price and then by descending estimate to break
# any ties. This produces "worst case" MKI/KI statistics, but ensures those
# statistics are deterministic. See this issue for more discussion:
# https://github.com/ccao-data/assesspy/issues/33#issuecomment-3180632954
df <- df[order(df$sp, -df$av), ]
assessed_price <- df$av
sale_price <- df$sp
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