Abstract—Composite risk scores that fuse supervised classifier
probabilities with unsupervised autoencoder reconstruction error
have recently been proposed to give fraud analysts a single
interpretable 0–100 triage signal. Existing composite-scoring
frameworks, however, combine these two signals through a single
fixed scalar weight tuned once by grid search, and explicitly leave
open whether a learned, context-aware fusion function would
perform better in practice. This paper implements and empir
ically evaluates that extension. We train a logistic-regression
meta-classifier over the outputs of a Random Forest classifier,
an XGBoost classifier, and an autoencoder anomaly detector
– augmented with transaction amount as a contextual feature
– and compare it against the fixed-weight composite baseline
on a held-out test partition preserving the extreme 0.172%
fraud rate of the ULB Credit Card Fraud benchmark. The
learned meta-fusion model strictly cost-dominates the standalone
Random Forest and XGBoost classifiers at every fraud-to-review
cost ratio, but does not uniformly dominate the fixed-weight
composite: a segment-level breakdown by transaction value shows
that meta-fusion wins decisively on low-value transactions while
the fixed-weight composite remains cost-optimal on mid- and
high-value transactions. Motivated by this finding, we propose a
segment-conditional deployment policy that applies meta-fusion
only to low-value transactions and the fixed-weight composite
elsewhere; this hybrid policy strictly dominates the fixed-weight
baseline and outperforms pure meta-fusion for essentially any
realistic cost ratio (r > 0.06). These results reframe fusion-layer
design not as a single global choice but as a segment-specific
operational decision, and provide financial institutions with a
concrete, reproducible protocol for deriving one.
Index Terms—Credit Card Fraud Detection, Score-Level Fu
sion, Meta-Classifier, Random Forest, XGBoo
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