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Help me with the Best model for extreme class imbalance (6 normal, 1 abnormal)? Isolation Forest giving 1.9% FP, XGB/LGBM just overfit to 99.9% acc

This story is from 2026-09-06. It is preserved in the archive; the latest stories are on the live feed.

I don't have enough data but gotta train something anyway lol. Right now I've got an Isolation Forest giving ~1.9% false positive rate. Tried XGBoost/LightGBM too but they just hit 99.9% accuracy by predicting the majority class every time, basically overfit/useless, 0 recall on the actual abnormal…

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  1. 2026-09-06 04:36 · r/learnmachinelearning
    Help me with the Best model for extreme class imbalance (6 normal, 1 abnormal)? Isolation Forest giving 1.9% FP, XGB/LGBM just overfit to 99.9% acc

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