Add InHospitalMortalityTemporalMIMIC4 task for EMDOT temporal evaluation

[nskath]

Contributors

• Kunal Daftari (kunald2@illinois.edu)
• Navtej Kathuria (navtejk2@illinois.edu)
• Fatih Atlamaz (atlamaz2@illinois.edu)

Type of Contribution

Standalone Task (Option 3)

Original Paper

Zhou, H.; Chen, Y.; and Lipton, Z. C. 2023. Evaluating Model Performance in Medical Datasets Over Time. CHIL 2023. PMLR 209:498-508.

• Paper: https://proceedings.mlr.press/v209/zhou23a.html
• arXiv: https://arxiv.org/abs/2305.13426

High-Level Description

This PR adds InHospitalMortalityTemporalMIMIC4, a standalone task that tags each admission sample with its real (de-shifted) calendar year so that callers can partition data chronologically using the EMDOT framework.

The EMDOT paper shows that standard random train/test splits overestimate model performance by ignoring temporal distribution shift in clinical data. This task enables reproducing that finding on MIMIC-IV by:

• Extracting diagnosis codes, procedure codes, and drug names as bag-of-codes features
• Generating binary in-hospital mortality labels from hospital_expire_flag
• De-shifting MIMIC-IV's anonymized dates using anchor_year and anchor_year_group to recover real calendar years
• Supporting both all-historical and sliding-window training regimes via the admission_year field

The ablation script demonstrates that random splits yield ~0.986 AUROC while temporal splits starting from 2012 yield ~0.937, confirming the paper's core finding. Window size ablation (w=1,2,3,5) shows the recency vs sample-size tradeoff.

File Guide

File	Description
pyhealth/tasks/in_hospital_mortality_temporal_mimic4.py	Core task implementation
pyhealth/tasks/__init__.py	Added InHospitalMortalityTemporalMIMIC4 import
tests/core/test_mimic4_mortality_temporal.py	16 unit tests using synthetic mock patients
examples/mortality_prediction/mortality_mimic4_temporal_emdot.py	EMDOT ablation study script
docs/api/tasks/pyhealth.tasks.InHospitalMortalityTemporalMIMIC4.rst	API documentation
docs/api/tasks.rst	Added entry to Available Tasks toctree