Accelerated longitudinal designs: An overview of modelling, power, costs and handling missing data

Sally Galbraith, Jack Bowden, Adrian Mander*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

52 Citations (Scopus)
362 Downloads (Pure)

Abstract

Longitudinal studies are often used to investigate age-related developmental change. Whereas a single cohort design takes a group of individuals at the same initial age and follows them over time, an accelerated longitudinal design takes multiple single cohorts, each one starting at a different age. The main advantage of an accelerated longitudinal design is its ability to span the age range of interest in a shorter period of time than would be possible with a single cohort longitudinal design. This paper considers design issues for accelerated longitudinal studies. A linear mixed effect model is considered to describe the responses over age with random effects for intercept and slope parameters. Random and fixed cohort effects are used to cope with the potential bias accelerated longitudinal designs have due to multiple cohorts. The impact of other factors such as costs and the impact of dropouts on the power of testing or the precision of estimating parameters are examined. As duration-related costs increase relative to recruitment costs the best designs shift towards shorter duration and eventually cross-sectional design being best. For designs with the same duration but differing interval between measurements, we found there was a cutoff point for measurement costs relative to recruitment costs relating to frequency of measurements. Under our model of 30% dropout there was a maximum power loss of 7%.

Original languageEnglish
Pages (from-to)374-398
Number of pages25
JournalStatistical Methods in Medical Research
Volume26
Issue number1
Early online date20 Aug 2014
DOIs
Publication statusPublished - Feb 2017

Keywords

  • accelerated longitudinal design
  • cohort effect
  • dropout
  • mixed model

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