Joint modeling of performance and subjective reporting to assess sensitivity to drug-induced sleepiness

James Fiedler, Alan H. Feiveson, Matthew J. Hayat, Zalman Vaksman, Jason L. Boyd, Lakshmi Putcha

Research output: Contribution to journalArticlepeer-review


In an NASA ground study, two forms of cognitive tests were evaluated in terms of their sensitivity to sleepiness induced by the drug promethazine (PMZ). Performance for the two test modes (Y1 and Y2), PMZ concentration, and a self-reported sleepiness using the Karolinska Sleepiness Scale (KSS) were monitored for 12 h post dose. A problem arises when using KSS to establish an association between true sleepiness and performance because KSS scores are discrete and also because they tend to concentrate on certain values. Therefore, we define a latent sleepiness measure X* as an unobserved continuous random variable describing a subject's actual state of sleepiness. Under the assumption that drug concentration affects X *, which then affects Y1, Y2, and KSS, we use Bayesian methods to estimate joint equations that permit unbiased comparison of the performance measures' sensitivity to X*. The equations incorporate subject random effects and include a negativity constraint on subject-specific slopes of performance with respect to sleepiness.

Original languageEnglish (US)
Pages (from-to)2246-2259
Number of pages14
JournalStatistics in Medicine
Issue number21
StatePublished - Sep 20 2010


  • Bayesian analysis
  • Hierarchical Bayesian modeling
  • Latent variable
  • Ordered probit
  • WinBUGS

ASJC Scopus subject areas

  • Epidemiology
  • Statistics and Probability

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