title: Area socioeconomic status and mortality after coronary artery bypass graft surgery: the role of hospital volume.
abstract: BACKGROUND
  Individuals of low socioeconomic status (SES) have reduced access to coronary artery bypass graft surgery (CABG). It is unknown if low-SES CABG patients have reduced access to hospitals with better outcomes.
  
  
  METHODS
  We conducted a retrospective cohort analysis of the California CABG Mortality Reporting Program, consisting of individuals with zip code information who underwent CABG at participating hospitals in 1999-2000 (n = 18,961). Primary outcome measures were inhospital mortality after CABG; primary independent variables of interest were area-level SES, clinical risk factors, and hospital volume. We used 2-level hierarchical random-effects logit models to estimate the relationship between explanatory variables and inhospital mortality.
  
  
  RESULTS
  Within high-volume hospitals, patients of low-SES areas had greater mortality than those of mid- and high-SES areas (2.5% vs 1.5% vs 1.8%, P = .024). However, there was no relationship between SES and mortality in lower-volume hospitals. Contrary to expectations, individuals of high-SES areas (42%) underwent surgery at low-volume hospitals more often than patients of low-SES areas (28%, P < .001), although mortality at low-volume hospitals was greater than that at high-volume facilities (P < .001). Discrepancies were not explained by distance traveled.
  
  
  CONCLUSIONS
  Mortality after CABG is modified by both SES and hospital volume. Within high-volume hospitals, patients of low-SES areas fared worse than patients of higher-SES areas. Patients of high SES tended to have CABG surgery at low-volume hospitals where mortality was greater and therefore had higher mortality than expected.
authors.affiliation: Division of General Internal Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI, USA. cathkim@umich.edu
authors.forename: Catherine
authors.initials: C
authors.lastname: Kim
authors.forename: Ana V
authors.initials: AV
authors.lastname: Diez Roux
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Hofer
authors.forename: Brahmajee K
authors.initials: BK
authors.lastname: Nallamothu
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Bernstein
authors.forename: Mary A M
authors.initials: MA
authors.lastname: Rogers
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002140:California / Q000453:epidemiology; D001026:Coronary Artery Bypass / Q000401:mortality* / Q000706:statistics & numerical data; D005260:Female; D017052:Hospital Mortality; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012923:Social Class