Clustering bias undermines threshold guarantees in production ML systems
Researchers identify a critical gap in how machine learning systems validate threshold-based decisions when training data exhibits clustering. Conformal predictors, safety filters, and abstention gates all rely on calibration sets to guarantee performance rates, but assume independence that rarely holds in practice. Modern pipelines cluster examples by shared prompts, documents, or reasoning traces, violating this assumption. The work adapts classical survey statistics techniques from 1965 to quantify effective sample size under correlation, extending beyond their original use for averages. This matters because threshold guarantees in production systems may be significantly weaker than advertised when data dependencies go unaccounted for.62












