Could it be that older (more experienced) physicians are more likely to get assigned to patients with more complex or serious conditions?

(I don't mean to state the obvious but this wasn't made explicitly clear enough to me.)

Edit: My initial comment here is probably wrong based on the detailed section "Adjustment variables":

> Patient characteristics included age in five year increments, sex, race or ethnic group (non-Hispanic white, non-Hispanic black, Hispanic, other), primary diagnosis (diagnosis related group), 27 comorbidities (Elixhauser comorbidity index22), median household income of zip code (in 10ths), an indicator for dual Medicare-Medicaid coverage, day of the week of the admission date (to account for the possibility that severity of illness of patients could be higher on specific days of the week), and year indicators.