title: Impact of length of stay after coronary bypass surgery on short-term readmission rate: an instrumental variable analysis.
abstract: OBJECTIVE
  : To determine the effect of postoperative length of stay (LOS) on 30-day readmission after coronary artery bypass surgery.
  
  
  METHODS
  : We analyzed a final database consisting of Medicare claims of a cohort (N=157,070) of all fee-for-service beneficiaries undergoing bypass surgery during 2007-2008, the American Hospital Association annual survey file, and the rural urban commuting area file.
  
  
  METHODS
  : We regressed the probability of 30-day readmission on postoperative LOS using (1) a (naive) logit model that controlled for observed patient and hospital covariates only; and (2) a residual inclusion instrumental variable (IV) logit model that further controlled for unobserved confounding. The IV was defined using a measure of the hospital's risk-adjusted LOS for patients admitted for gastrointestinal hemorrhage.
  
  
  RESULTS
  : The naive logit model predicted that a 1-day reduction in median postoperative LOS (ie, from a median of 6-5 d) lowered the 30-day readmission rate by 2 percentage points. The IV model predicted that a 1-day reduction in median postoperative LOS increased 30-day readmission rate by 3 percentage points.
  
  
  CONCLUSIONS
  : The findings indicate that a reduction in postoperative LOS is associated with an increased risk for 30-day readmission among Medicare patients undergoing bypass surgery, after both observed and unobserved confounding effects are corrected.
authors.affiliation: Department of Community and Preventive Medicine, Division of Health Policy and Outcomes Research, University of Rochester, Rochester, NY 14642, USA. yue_li@urmc.rochester.edu
authors.forename: Yue
authors.initials: Y
authors.lastname: Li
authors.forename: Xueya
authors.initials: X
authors.lastname: Cai
authors.forename: Dana B
authors.initials: DB
authors.lastname: Mukamel
authors.forename: Peter
authors.initials: P
authors.lastname: Cram
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001026:Coronary Artery Bypass / Q000706:statistics & numerical data*; D006761:Hospitals / Q000706:statistics & numerical data; D006801:Humans; D007345:Insurance Claim Review / Q000706:statistics & numerical data; D007902:Length of Stay / Q000706:statistics & numerical data*; D016015:Logistic Models; D006278:Medicare / Q000706:statistics & numerical data; D010359:Patient Readmission / Q000706:statistics & numerical data*; D011787:Quality of Health Care / Q000706:statistics & numerical data; D012307:Risk Factors; D012737:Sex Factors; D013997:Time Factors; D014481:United States