Version Compatibility

Reference examples tested with: numpy 1.26+, scikit-learn 1.4+ (note 1.6/1.8 API changes below).

Before using code patterns, verify installed versions match. If versions differ:

• Python: pip show <package> then help(module.function) to check signatures

scikit-learn drift to watch: CalibratedClassifierCV(cv='prefit') was deprecated in 1.6 and removed in 1.8 (it now raises; wrap a fitted model in sklearn.frozen.FrozenEstimator instead); ensemble default became 'auto' in 1.6; method='temperature' was added in 1.8. If code throws ImportError, AttributeError, or TypeError, introspect the installed package and adapt the example to match the actual API rather than retrying.

Model Validation for Biomedical and Omics Data

"Validate my omics classifier honestly" -> Keep every data-dependent step inside the resampling loop, never use the same data to both choose and grade, and report calibration and net benefit, not just AUC.

• Nested CV: GridSearchCV (inner) wrapped by cross_val_score (outer)
• Group/structured: StratifiedGroupKFold, TimeSeriesSplit
• Calibration: calibration_curve, brier_score_loss, CalibratedClassifierCV

The Single Most Important Modern Insight -- A Reported Number Is an Honest Estimate Only If Nothing Leaked and Nothing Was Graded on What Was Chosen

A reported performance number is a claim about a data-generating process that will never recur. Almost every inflated result in ML-for-biology traces to one of two root causes: information from the test distribution leaked into model construction, or the same data was used to both choose and grade a decision. A clean train/test split is necessary but nowhere near sufficient -- the leakage has usually already contaminated the test set (a scaler fit on all data, a duplicate patient, ComBat run across the split). Leakage causes a reproducibility crisis across ML-based science (Kapoor 2023), and the bias is largest exactly when the true signal is weakest -- the omics regime.