Analysis of longitudinal data with irregular, outcome-dependent follow-up

Haiqun Lin, Daniel O. Scharfstein, Robert A. Rosenheck

Research output: Contribution to journalArticlepeer-review

98 Scopus citations


A frequent problem in longitudinal studies is that subjects may miss scheduled visits or be assessed at self-selected points in time. As a result, observed outcome data may be highly unbalanced and the availability of the data may be directly related to the outcome measure and/or some auxiliary factors that are associated with the outcome. If the follow-up visit and outcome processes are correlated, then marginal regression analyses will produce biased estimates. Building on the work of Robins, Rotnitzky and Zhao, we propose a class of inverse intensity-of-visit process-weighted estimators in marginal regression models for longitudinal responses that may be observed in continuous time. This allows us to handle arbitrary patterns of missing data as embedded in a subject's visit process. We derive the large sample distribution for our inverse visit-intensity-weighted estimators and investigate their finite sample behaviour by simulation. Our approach is illustrated with a data set from a health services research study in which homeless people with mental illness were randomized to three different treatments and measures of homelessness (as percentage days homeless in the past 3 months) and other auxiliary factors were recorded at follow-up times that are not fixed by design.

Original languageEnglish (US)
Pages (from-to)791-813
Number of pages23
JournalJournal of the Royal Statistical Society. Series B: Statistical Methodology
Issue number3
StatePublished - 2004
Externally publishedYes


  • Counting process
  • Drop-out
  • Health service evaluation
  • Intermittent missingness
  • Longitudinal data
  • Non-gaussian data
  • Semiparametric estimators
  • Sequential ignorability
  • Visit process
  • Weighted generalized estimating equations

ASJC Scopus subject areas

  • Statistics and Probability
  • Statistics, Probability and Uncertainty


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