title: The ecological fallacy of the role of age in chronic disease and hospital demand.
abstract: OBJECTIVE
  To examine the relationship between age and all-cause hospital utilization in the years preceding and following a diagnosis in hospital of heart failure, type 2 diabetes, or chronic obstructive pulmonary disease (COPD).
  
  
  METHODS
  A cohort study of all patients in Western Australia who have had a principal diagnosis of heart failure, type 2 diabetes, or COPD, upon admission to hospital. All-cause hospital utilization 6 years preceding and 4 years following cardinal events, that is, a disease-specific diagnosis upon hospital admission, where such an event has not occurred in the previous 2 years, are examined in specific age groups.
  
  
  RESULTS
  Six years preceding a cardinal event, all-cause emergency department (ED) presentations are similar in all age groups, from under 55 to over 85 years of age, except in COPD where ED presentation rates are higher in younger groups. All-cause hospital inpatient days are transiently higher in the years preceding and following a cardinal event in older age groups, yet return to similar levels across all age cohorts after 4 years. ED presentations are significantly higher in the 4 years following cardinal events in younger compared with older groups.
  
  
  CONCLUSIONS
  Longitudinal analysis of utilization around cardinal events overcomes the confounding effect of differences in chronic disease rates between age groups, avoiding a source of ecologic bias that erroneously attributes increasing utilization in individuals with chronic disease to age. Programs designed to reduce hospital demand in patients with chronic disease should possibly focus on younger, rather than older, individuals.
authors.affiliation: *School of Primary, Aboriginal, and Rural Health Care, Faculty of Medicine, Dentistry and Health Sciences †School of Mathematics and Statistics, Faculty of Engineering, Computing and Mathematics ‡School of Population Health, Faculty of Medicine, Dentistry and Health Sciences, The University of Western Australia, Crawley, WA §Illawarra Health and Medical Research Institute, University of Wollongong, Haymarket, NSW, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Whyatt
authors.forename: Raji
authors.initials: R
authors.lastname: Tenneti
authors.forename: Julie
authors.initials: J
authors.lastname: Marsh
authors.forename: Anna
authors.initials: A
authors.lastname: Kemp
authors.forename: Laura
authors.initials: L
authors.lastname: Firth
authors.forename: Kevin
authors.initials: K
authors.lastname: Murray
authors.forename: Berwin
authors.initials: B
authors.lastname: Turlach
authors.forename: Alistair
authors.initials: A
authors.lastname: Vickery
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D002908:Chronic Disease; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000628:therapy*; D004632:Emergency Medical Services / Q000706:statistics & numerical data*; D005260:Female; D006301:Health Services Needs and Demand / Q000706:statistics & numerical data*; D006333:Heart Failure / Q000628:therapy*; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000628:therapy*; D014904:Western Australia