aiDIF: Differential Item Functioning for AI-Scored Assessments

Overview

aiDIF addresses a modern measurement fairness challenge: does AI scoring introduce subgroup-dependent item bias?

As AI systems increasingly score essays, short answers, and structured responses in educational and psychological assessments, a critical question arises: does the AI scoring engine shift item difficulties differently for different demographic groups — even when no human-scoring DIF exists?

aiDIF provides:

• Robust DIF analysis under both human and AI scoring conditions, using a fully self-contained M-estimation engine (IRLS with bi-square loss)
• Differential AI Scoring Bias (DASB) test — a novel Wald test for item-level scoring shifts that differ across groups
• AI-effect summaries classifying items as: stable_clean, stable_dif, introduced, masked, or new_direction across scoring conditions
• Anchor weight diagnostics under potential AI contamination
• Simulation utilities for benchmarking DIF methods in AI-scored settings

Installation

# Install from GitHub
devtools::install_github("causalfragility-lab/aiDIF")

# Or install from local source
devtools::install_local("path/to/aiDIF")

Quick Start

library(aiDIF)

# Generate synthetic data with known DIF and DASB
dat <- simulate_aidif_data(n_items = 6, seed = 1)

# Fit the model
mod <- fit_aidif(
  human_mle = dat$human,
  ai_mle    = dat$ai
)

# Compact summary
print(mod)

# Full report
summary(mod)

# Visualisations
plot(mod, type = "dif_forest")  # Forest plot: human vs AI DIF estimates
plot(mod, type = "dasb")        # Bar chart of DASB with error bars
plot(mod, type = "weights")     # Anchor weights in each scoring condition
plot(mod, type = "rho")         # Bi-square objective for human scoring

Core Concepts

Differential AI Scoring Bias (DASB)

For item i and group g, define the scoring shift:

delta_ig = d_ig^AI - d_ig^Human

where d_ig is the IRT intercept (difficulty) parameter. The DASB is:

DASB_i = delta_i2 - delta_i1

Under H₀: DASB_i = 0, a Wald test is conducted using the asymptotic variance derived from the delta method (assuming independent groups and scoring conditions):

Var(DASB_i) = Var(d_i1^H) + Var(d_i2^H) + Var(d_i1^AI) + Var(d_i2^AI)

A significant result means the AI scoring engine does not merely re-scale all items uniformly — it disadvantages (or advantages) one group at specific items.

AI-Effect Classification

ai_effect_summary() compares DIF flagging patterns between scoring conditions:

Status	Meaning
stable_clean	Not flagged in either condition
stable_dif	Flagged in both (same direction)
introduced	Flagged only under AI scoring
masked	Flagged only under human scoring
new_direction	Flagged in both, but bias reverses sign

From Existing IRT Fits

If you have fitted IRT models in mirt, use read_ai_scored() to bundle your parameter estimates into the format fit_aidif() expects:

library(mirt)

# Fit multigroup 2PL under human scoring
human_fit <- mirt(human_data, model = 1, itemtype = "2PL",
                  group = "group", SE = TRUE)

# Extract parameters manually and bundle
# (see ?read_ai_scored for the required list structure)
dat <- read_ai_scored(human_mle, ai_mle)

# Fit aiDIF model
mod <- fit_aidif(dat$human, dat$ai)

Simulation

# Generate synthetic data with known DIF and DASB
dat <- simulate_aidif_data(
  n_items    = 10,
  n_obs      = 500,
  impact     = 0.5,      # 0.5 SD group mean difference
  dif_items  = c(1, 2),  # items with human-scoring DIF
  dif_mag    = 0.5,
  dasb_items = 5,        # item with AI-induced differential bias
  dasb_mag   = 0.4,
  ai_drift   = 0.1       # uniform AI calibration offset
)

mod <- fit_aidif(dat$human, dat$ai)
summary(mod)

Package Architecture

aiDIF/
├── R/
│   ├── read_functions.R    # read_ai_scored()
│   ├── aidif_core.R        # fit_aidif() — main estimation wrapper
│   ├── robust_engine.R     # estimate_robust_scale(), Wald tests, IRLS engine
│   ├── scoring_bias.R      # scoring_bias_test(), ai_effect_summary(),
│   │                       #   anchor_weights()
│   ├── simulate.R          # simulate_aidif_data()
│   ├── validate_inputs.R   # Internal validation helpers
│   └── class_functions.R   # print/summary/plot S3 methods
├── tests/
│   └── testthat/
│       └── test-aidif.R
└── DESCRIPTION

Citation

If you use aiDIF in published research, please cite:

Hait, S. (2026). aiDIF: Differential Item Functioning for AI-Scored
Assessments. R package version 0.1.0.
https://github.com/causalfragility-lab/aiDIF

License

GPL (>= 3)