Physician's preference-based instrumental variable analysis: is it valid and useful in a moderate-sized study?

Background: Instrumental variable methods can potentially circumvent the unmeasured confounding inherent in observational data analyses.

Methods: We investigated the validity and usefulness of physician's preference instrumental variable analysis in the setting of a moderate-sized clinical study. Using routine care data from 476 elective cardiac surgery patients, we assessed the effect of preoperative corticosteroids on mechanical ventilation time and duration of intensive care and hospital stay, occurrence of infections, atrial fibrillation, heart failure, and delirium.