Statistical measures were proposed for identifying longitudinal patterns of change in quantitative health indicators.
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.
Leffondré
Karen
K
Department of Epidemiology and Biostatistics, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
Abrahamowicz
Michal
M
Regeasse
Armelle
A
Hawker
Gillian A
GA
Badley
Elizabeth M
EM
McCusker
Jane
J
Belzile
Eric
E
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