title: Statistical measures were proposed for identifying longitudinal patterns of change in quantitative health indicators.
abstract: OBJECTIVE
  To propose statistical measures to identify different longitudinal patterns of change in quantitative health indicators.
  
  
  METHODS
  The authors propose several simple measures to discriminate between stable-unstable, increasing-decreasing, linear-nonlinear, monotonic-nonmonotonic patterns of change. They then suggest using factor analysis to select the subset of nonredundant measures, and cluster analysis, based on the selected measures, to identify subgroups of patients with similar longitudinal trajectories. The proposed approach is illustrated using data on osteoarthritis disability from a longitudinal study undertaken in Toronto, Ontario, in 1996-2001. Disability was measured at four points in time for 835 patients, using the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index.
  
  
  RESULTS
  The proposed measures allowed the detection of individual patients with specific patterns of change and identification of four different groups of patients with WOMAC scores that are (1) regularly increasing, (2) regularly decreasing, (3) stable over time, or (4) highly unstable, with abrupt changes or short-term fluctuations.
  
  
  CONCLUSIONS
  The proposed approach may be used to (1) screen even large databases to identify particular patterns of change; or (2) summarize different patterns of change by classifying patients into groups with similar trajectories. Once identified, the groups can be investigated to determine whether there are differences in patient characteristics or outcomes.
authors.affiliation: Department of Epidemiology and Biostatistics, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
authors.forename: Karen
authors.initials: K
authors.lastname: Leffondré
authors.forename: Michal
authors.initials: M
authors.lastname: Abrahamowicz
authors.forename: Armelle
authors.initials: A
authors.lastname: Regeasse
authors.forename: Gillian A
authors.initials: GA
authors.lastname: Hawker
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Badley
authors.forename: Jane
authors.initials: J
authors.lastname: McCusker
authors.forename: Eric
authors.initials: E
authors.lastname: Belzile
mesh_terms: D000368:Aged; D002908:Chronic Disease; D016000:Cluster Analysis; D006305:Health Status Indicators; D006801:Humans; D008137:Longitudinal Studies; D015233:Models, Statistical; D010003:Osteoarthritis / Q000503:physiopathology* / Q000523:psychology; D012680:Sensitivity and Specificity