title: Effects on preferences of violations of procedural invariance.
abstract: BACKGROUND
  In studies of health preferences, utilities for hypothetical health states cannot always be successfully measured. One marker for unsuccessful measurement is violation of "procedural invariance": when the ranking of two health states varies across assessment procedures. Using preference values based on unsuccessful measurement may result in misinterpretation of patients' attitudes about health.
  
  
  OBJECTIVE
  The authors sought to determine whether people who violated procedural invariance had different preferences than people who satisfied it.
  
  
  METHODS
  They performed secondary analyses of three completed studies that used the same two assessment procedures, identifying participants who violated procedural invariance and comparing the mean standard gamble (SG) and visual analog scale (VAS) scores of violators and satisfiers.
  
  
  METHODS
  Experiment 1, 30 healthy volunteers and 30 patients with cardiac arrhythmias; experiment 2, 139 patients with depressive illness; experiment 3, 98 family members of patients with schizophrenia.
  
  
  RESULTS
  Rates of violation of procedural invariance ranged from 16% to 32%. Violation of procedural invariance was not associated with age, education level, race, or gender. Subjects with violations of procedural invariance had, in general, less ability to discriminate among states and less reliable VAS and SG measurements, and sometimes had different mean SG and VAS values.
  
  
  CONCLUSIONS
  Violation of procedural invariance of preferences across scaling methods may be a signal for failure of the measurement process. Researchers should test for procedural invariance and consider reporting data separately for satisfiers and violators.
authors.affiliation: Health Services Research and Development, Veterans Affairs San Diego Healthcare System, California 92161, USA. llenert@uscd.edu
authors.forename: L A
authors.initials: LA
authors.lastname: Lenert
authors.forename: J R
authors.initials: JR
authors.lastname: Treadwell
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000523:psychology*; D001294:Attitude to Health; D003201:Computers; D003362:Cost-Benefit Analysis; D003661:Decision Support Techniques; D003866:Depressive Disorder / Q000523:psychology*; D004522:Educational Status; D005190:Family / Q000523:psychology; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D017060:Patient Satisfaction; D012559:Schizophrenia