Inference of nested variance components in a longitudinal myopia intervention trial

Chuhsing Kate Hsiao, Miao-Yu Tsai, Ho Min Chen

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


This paper was motivated by a double-blind randomized clinical trial of myopia intervention. In addition to the primary goal of comparing treatment effects, we are concerned with the modelling of correlation that may come from two possible sources, one among the longitudinal observations and the other between measurements taken from both eyes per subject. The data are nested repeated measurements. We suggest three models for analysis. Each one expresses the correlation differently in various covariance structures. We articulate their differences and describe the implementations in estimation using commercial statistical software. The computer output can be further utilized to perform model selection with Schwarz criterion. Simulation studies are conducted to evaluate the performance under each model. Data of the myopia intervention trial are reanalysed with these models for illustration. The results indicate that atropine is more effective in reducing the progression rate, the rates are homogeneous across subjects, and, among the suggested models, the one with independent random effects of two eyes fits best. We conclude that model selection is a crucial step before making inference with estimates; otherwise the correlation may be attributed incorrectly to a different mechanism. The same conclusion applies to other variance components as well.

Original languageEnglish
Pages (from-to)3251-3267
Number of pages17
JournalStatistics in Medicine
Issue number21
Publication statusPublished - 2005 Nov 15

All Science Journal Classification (ASJC) codes

  • Epidemiology
  • Statistics and Probability

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