Coursework 06 · this term
The part
everyone skips.
Applied Data Science, Fall 2026. The brief hands you three sources for a hospital readmission problem: a patient table, a nested clinical JSON, an engagement export. Merging them into 2,507 visits across 800 patients is the easy half. The half that decides whether a model means anything is the order of operations.
So the holdout was cut first, by patient and not by visit, before a single imputer saw the data. The cost cap came from the training rows alone, $47,026.98, then was applied unchanged to the test rows. And the missingness was diagnosed instead of assumed: BMI is missing on 54.84% of visits at the older clinics and 0.00% at the newer ones, which is what a mechanism looks like when you can actually see it. The stakeholder's theory, that satisfaction scores went missing because unhappy patients stayed quiet, did not survive contact with the data, so it stayed a working assumption rather than a finding.