Bias Amplification Score (parity gap x Gini of group rates)

BAS = delta_parity * G, where delta_parity is the demographic-parity gap of the worst-affected group and G is the Gini coefficient of the per-group favourable-outcome rates. Large only when a directional disparity coincides with high cross-group inequality.

Usage

morie_fairness_bias_amplification(
  y_pred,
  group,
  privileged = NULL,
  favorable = 1
)

Arguments

y_pred

Vector of decisions / assignments per individual.

group

Protected-attribute vector aligned with y_pred.

privileged

Reference group. If NULL, the highest-rate group is inferred and a warning is emitted.

favorable

Value of y_pred that counts as favourable (default 1).

Value

A morie_fairness_result; headline value is BAS.

Details

Reimplemented from Barman & Barman, arXiv:2603.18987.

Examples

morie_fairness_bias_amplification(
  c(1, 1, 1, 1, 0, 0, 0, 0),
  c(rep("A", 4), rep("B", 4)),
  privileged = "A"
)
#> Bias Amplification Score
#> ========================
#>   Bias Amplification Score  -0.5
#>   Demographic parity gap    -1
#>   Gini of group rates       0.5
#>   Reference group           A
#> 
#> Bias Amplification Score = -0.5000 (parity gap -1.000 x Gini 0.500). Both a directional disparity and substantial cross-group inequality are present - the system amplifies bias.