Heterogeneity's ruses: the neglected role of between-individual variability in longitudinal studies of COPD exacerbations.
Bottom Line: Standard survival analysis techniques often used in such studies typically produce results that pertain to the overall population, whereas the greatest interest is in the study of associations within individuals.A factor that can lead to profound discrepancies between population-level and individual-level survival patterns is the between-individual heterogeneity in the rate of exacerbations.We caution on the distinction between population and individual-level associations in survival analysis, and recommend accounting for heterogeneity in future studies.
Affiliation: Faculty of Medicine, Institute for Heart and Lung Health, The University of British Columbia, Vancouver, British Columbia, Canada.Show MeSH
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Mentions: There is great interest in studying the impact of exacerbations on the course of COPD. Such studies often rely on survival analysis of longitudinal data. Standard survival analysis techniques produce results that pertain to the population, whereas the real interest is in within-individual associations. A crucial issue in this context is the heterogeneity in the exacerbation rate across individuals. Estimates of hazard function from survival analysis are particularly associated with surprisingly conflicting and potentially misleading patterns when heterogeneity is not taken into account.1figure 1 provides an illustrative example.
Affiliation: Faculty of Medicine, Institute for Heart and Lung Health, The University of British Columbia, Vancouver, British Columbia, Canada.