title: Physician's preference-based instrumental variable analysis: is it valid and useful in a moderate-sized study?
abstract: 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.
  
  
  RESULTS
  Although results of the physician's preference-based instrumental variable analysis corresponded in direction to results of a recent large randomized trial of the same therapy, the instrumental variable estimates showed much larger effects with very wide confidence intervals.
  
  
  CONCLUSIONS
  The lesser statistical precision limits the usefulness of instrumental variable analysis in a study that might be of sufficient size for conventional analyses, even if a strong and plausible instrument is available.
authors: From the aDepartment of Clinical Epidemiology; bDepartment of Intensive Care; cDepartment of Medical Statistics and Bioinformatics; and dDepartment of Endocrinology and Metabolic Diseases, Leiden University Medical Centre, Leiden, The Netherlands.
authors: Anna G C
authors: AG
authors: Boef
authors: Judith
authors: J
authors: van Paassen
authors: M Sesmu
authors: MS
authors: Arbous
authors: Arno
authors: A
authors: Middelkoop
authors: Jan P
authors: JP
authors: Vandenbroucke
authors: Saskia
authors: S
authors: le Cessie
authors: Olaf M
authors: OM
authors: Dekkers
mesh_terms: D000305:Adrenal Cortex Hormones / Q000008:administration & dosage*; D000368:Aged; D001281:Atrial Fibrillation / Q000453:epidemiology; D006348:Cardiac Surgical Procedures; D016001:Confidence Intervals; D015986:Confounding Factors, Epidemiologic; D003693:Delirium / Q000453:epidemiology; D004812:Epidemiologic Methods; D005260:Female; D006333:Heart Failure / Q000453:epidemiology; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data*; D012107:Research Design; D012121:Respiration, Artificial / Q000706:statistics & numerical data; D013530:Surgical Wound Infection / Q000453:epidemiology; D013997:Time Factors
chemical_list: D000305:Adrenal Cortex Hormones