Theory 04/The rival is a confound/Hospitals
Staffing or Case Mix?
The claim
Readmission rates reflect discharge-day staffing rather than patient complexity.
01The rival explanation
Hospitals with low weekend staffing also serve sicker or more deprived populations, so the association is compositional.
02What would tell them apart
Within-hospital variation across days of the week holds case mix roughly constant while staffing varies.
03Prediction
Readmission should vary by discharge day within the same hospital.
04Refutation
If within-hospital variation is absent, the rival wins.