title: Do longer postpartum stays reduce newborn readmissions? Analysis using instrumental variables.
abstract: OBJECTIVE
  To determine the effect of postpartum length of stay on newborn readmission.
  
  
  METHODS
  Secondary data set consisting of newborns born in Washington state in 1989 and 1990. The data set contains information about the characteristics of the newborn and its parents, physician, hospital, and insurance status.
  
  
  METHODS
  Analysis of the effect of length of stay on the probability of newborn readmission using hour of birth and method of delivery as instrumental variables (IVs) to account for unobserved heterogeneity. Of approximately 150,000 newborns born in Washington in 1989 and 1990, 108,551 (72 percent) were included in our analysis.
  
  
  RESULTS
  Newborns with different lengths of stay differ in unmeasured characteristics, biasing estimates based on standard statistical methods. The results of our analyses show that a 12-hour increase in length of stay is associated with a reduction in the newborn readmission rate of 0.6 percentage points. This is twice as large as the estimate obtained using standard statistical (non-IV) methods.
  
  
  CONCLUSIONS
  An increase in the length of postpartum hospital stays may result in a decline in newborn readmissions. The magnitude of this decline in readmissions may be larger than previously thought.
authors.affiliation: Covance Health Economics and Outcomes Services Inc., Gaithersburg, MD 20878-5355, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Malkin
authors.forename: M S
authors.initials: MS
authors.lastname: Broder
authors.forename: E
authors.initials: E
authors.lastname: Keeler
mesh_terms: D015982:Bias; D003627:Data Interpretation, Statistical; D036861:Delivery, Obstetric / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D006302:Health Services Research / Q000379:methods*; D006801:Humans; D007231:Infant, Newborn; D007348:Insurance, Health / Q000706:statistics & numerical data; D016018:Least-Squares Analysis; D007902:Length of Stay / Q000706:statistics & numerical data*; D008297:Male; D017533:Marital Status / Q000706:statistics & numerical data; D017059:Models, Econometric; D009010:Monte Carlo Method; D010298:Parity; D010359:Patient Readmission / Q000706:statistics & numerical data*; D018743:Perinatal Care / Q000706:statistics & numerical data*; D013997:Time Factors; D014861:Washington