title: The impact of surgeon specialization on patient mortality: examination of a continuous Herfindahl-Hirschman index.
abstract: OBJECTIVE
  To examine the effect of surgeon specialization on patient outcomes, controlling for volume.
  
  
  BACKGROUND
  There is great interest in the degree to which surgical specialization affects outcomes, particularly considering drives to measure and reward quality in healthcare. Although surgical specialization has been previously analyzed with respect to outcomes, most studies have treated it as a dichotomous variable based on academic credentials. We treat it here as a continuous variable defined quantitatively by procedural diversity.
  
  
  METHODS
  We used 2002 to 2005 patient data from the National Surgical Quality Improvement Program for the Department of Surgery, Barnes Jewish Hospital, St. Louis, Missouri. To quantitate procedural specialization, Herfindahl-Hirschman indices for surgeons were calculated using billing codes. These indices were calculated according to 3 different levels of procedural aggregation. Using conditional logit models, we examined the relationship between these indices and 30-day postoperative mortality rates.
  
  
  RESULTS
  Surgeon specialization was inversely related to mortality rates after adjusting for case volume when indices were calculated using medium procedural aggregation (odds ratio for mortality = 0.580 per 0.1 unit Herfindahl increase; P = 0.025) or low aggregation (odds ratio for mortality = 0.510 per 0.1 unit Herfindahl increase; P = 0.015). No relationship was observed at the high level of aggregation.
  
  
  CONCLUSIONS
  The procedural concentration component of surgical specialization is correlated with improved mortality rates independently of case volume. However, how broadly or narrowly "specialization" is defined has an impact on this relationship.
authors.affiliation: Department of Surgery, John Cochran Veterans Affairs Medical Center, St Louis, Missouri, USA. hallb@ wustl.edu
authors.forename: Bruce Lee
authors.initials: BL
authors.lastname: Hall
authors.forename: Esther Y
authors.initials: EY
authors.lastname: Hsiao
authors.forename: Sarah
authors.initials: S
authors.lastname: Majercik
authors.forename: Mitzi
authors.initials: M
authors.lastname: Hirbe
authors.forename: Barton H
authors.initials: BH
authors.lastname: Hamilton
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D013043:Specialties, Surgical / Q000706:statistics & numerical data*