Joint Meeting of the Royal Statistical Society Avon local group and LEMMA
node of the National Centre for Research Methods
“Mood Changes Associated with Smoking in Adolescents: Applications of
Mixed-Effects Location Scale Models for Cross-Sectional and Longitudinal
Ecological Momentary Assessment (EMA) Data”
Don Hedeker (Professor of Biostatistics, University of Illinois)
DATE: Tuesday 26 February
TIME: 4-5pm (tea/coffee at 3.30pm)
LOCATION: School of Geographical Sciences (room tbc), University of Bristol
REGISTRATION AND QUERIES: This event is open to all. There is no fee but
please register your attendance using the online booking form:
http://www.bris.ac.uk/cmm/software/mlwin/support/workshops/bookingseminar.html.
The event is expected to be very popular - please ensure you are able to
attend and let us know if you are unable to use your place so we can offer
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ABSTRACT:
For longitudinal data, mixed models include random subject effects to
indicate how subjects influence their responses over the repeated
assessments. The error variance and the variance of the random effects are
usually considered to be homogeneous. These variance terms characterize
the within-subjects (error variance) and between-subjects (random-effects
variance) variation in the data. In studies using Ecological Momentary
Assessment (EMA), up to thirty or forty observations are often obtained for
each subject, and interest frequently centres around changes in the
variances, both within- and between- subjects. Also, such EMA studies
often include several waves of data collection.
In this presentation, we focus on an adolescent smoking study using EMA at
both one and several measurement waves, where interest is on characterizing
changes in mood variation associated with smoking. We describe how
covariates can influence the mood variances, and also describe an extension
of the standard mixed model by adding a subject-level random effect to the
within-subject variance specification. This permits subjects to have
influence on the mean, or location, and variability, or (square of the)
scale, of their mood responses. Additionally, we allow the location and
scale random effects to be correlated. These mixed-effects location scale
models have useful applications in many research areas where interest
centres on the joint modeling of the mean and variance structure.
ABOUT THE SPEAKER:
Professor Don Hedeker is an international leader in the development and
application of multilevel models for longitudinal and clustered data. He is
the primary author of the popular ‘Longitudinal Data Analysis’ graduate
textbook and the SuperMix mixed-effects software. He is a Fellow of the
American Statistical Association, associate editor for Statistics in
Medicine and the Journal of Statistical Software, and the author of
numerous peer-reviewed papers.
www.ihrp.uic.edu/researcher/donald-hedeker-phd.
This event is sponsored by the LEMMA node of the ESRC National Centre for
Research Methods (http://www.bris.ac.uk/cmm/research/lemma/3/).
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