title: Composite outcomes: weighting component events according to severity assisted interpretation but reduced statistical power.
abstract: OBJECTIVE
  In trials of chronic disease therapy, each patient may experience several nonfatal illnesses and death. "Composite" outcome measures combine information from these different components of disease burden. Most common is the binary distinction between patients undergoing one or more events and those undergoing no events. We compare this approach with a composite score that preserves information on the number and severity of events.
  
  
  METHODS
  The binary composite measure and composite score were derived for each patient in a trial of cardiovascular therapy. All nonfatal events contributed to the composite score according to their severity: recurrent myocardial infarction (weight 0.5), congestive heart failure that required the use of open-label angiotensin-converting enzyme (ACE) inhibitors (weight 0.2), and hospitalization to treat congestive heart failure (weight 0.5).
  
  
  RESULTS
  In the example data set, the composite score required a 10% larger sample size to achieve the same power as the binary measure. However, the composite score suggested that the treatment impacted on the first nonfatal event and mortality only.
  
  
  CONCLUSIONS
  The composite score provides a more informative measure of disease burden and may avoid overestimating the evidence supporting a treatment effect when that evidence is largely from less severe early events.
authors.affiliation: Division of Cardiovascular Medicine, Vanderbilt University Medical Center, and Meharry Medical College, Nashville, TN 37232, USA. uchechukwu.sampson@vanderbilt.edu
authors.forename: Uchechukwu K A
authors.initials: UK
authors.lastname: Sampson
authors.forename: Chris
authors.initials: C
authors.lastname: Metcalfe
authors.forename: Marc A
authors.initials: MA
authors.lastname: Pfeffer
authors.forename: Scott D
authors.initials: SD
authors.lastname: Solomon
authors.forename: Kelly H
authors.initials: KH
authors.lastname: Zou
mesh_terms: D002318:Cardiovascular Diseases / Q000453:epidemiology*; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data; D023381:Endpoint Determination; D006801:Humans; D009203:Myocardial Infarction / Q000453:epidemiology*; D016017:Odds Ratio; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data*; D012107:Research Design; D012720:Severity of Illness Index