title: Measuring unexplained variation in acute hospital use by patients enrolled with northern New Zealand general practices.
abstract: BACKGROUND
  There is increasing concern worldwide at the steady growth in acute inpatient admissions and emergency department (ED) attendances.
  
  
  OBJECTIVE
  To develop measures of variation in acute hospital use between populations enrolled at different general practices that are independent of the sociodemographic characteristics of those populations.
  
  
  METHODS
  Two consecutive years of hospital discharge and ED attendance data were combined with primary health organisation (PHO) registers from 385 practices of over 1.5 million people to develop and test two measures of unplanned hospital use: the standardised acute hospital admission ratio (SAAR) and the standardised ED attendance ratio (SEAR). Disease-specific measures were also produced for inpatient events.
  
  
  RESULTS
  The enrolled populations of a high proportion of practices had significantly higher or lower than expected acute use of hospitals and this was consistent over both years studied. Practices whose population made unexpectedly high use of acute hospital care for one condition tended to do so for others. Differences in health needs between practice populations as measured by clinical complexity, comorbidities and length of stay did not explain a significant portion of the overall variation in hospital admissions. The enrolled population's average travelling time to a 24-hour ED accounted for some of the practice variation in unplanned utilisation of hospital services.
  
  
  CONCLUSIONS
  This study confirms that there is considerable unexplained practice variation in acute hospital use. Further development of the SAAR and SEAR measures may be possible to use these to identify modifiable practice-level factors associated with high unplanned hospital use.
authors.affiliation: Waitemata District Health Board, Level 1, 15 Shea Tce, Takapuna, Auckland 0740, New Zealand. Peter.sandiford@waitematadhb.govt.nz.
authors.forename: Peter
authors.initials: P
authors.lastname: Sandiford
authors.affiliation: Planning and Funding, Waitemata District Health Board, Auckland, New Zealand.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Waitemata Primary Health Organisation, Auckland.
authors.forename: Micol
authors.initials: M
authors.lastname: Salvetto
authors.affiliation: Waitemata Primary Health Organisation, Auckland.
authors.forename: Lannes F
authors.initials: LF
authors.lastname: Johnson
mesh_terms: D016208:Databases, Factual; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D058006:General Practice; D006301:Health Services Needs and Demand / Q000706:statistics & numerical data; D017721:Hospital Costs; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D009520:New Zealand; D010351:Patient Discharge; D012017:Referral and Consultation / Q000706:statistics & numerical data*