The following Departmental seminar will take place on Wed 23rd June at
2pm in the Levinsky Room, UCL Institute of Child Health, 30 Guilford
Street, London WC1N 1EH. All welcome.
Professor Jane Hutton (University of Warwick)
"Modelling health scores with the multivariate skew normal"
Abstract
Health care interventions which use quality of life or health scores
often provide data which are skewed and bounded. The scores are
typically formed by adding up responses to a number of questions.
Different questions might have different weights, but the score will be
bounded, and might be scaled to the range 0 to 100. If improvement in
health over time is measured, scores will tend to cluster near the
'healthy' or 'good' boundary as time progresses, leading to a skew
distribution. Further, some patients will drop out as time progresses,
so the scores reflect a selected population.
We fit multivariate skew normal distributions to data from a randomised
controlled trial of four treatments for sprained ankles, in which scores
were recorded at baseline and 1, 3 and 9 months. In these data, the
scores at 3 and 9 months have skew marginal distributions, but the
variance is similar across the four times points. We consider the extent
to which variance and skewness can be explained by covariates including
treatment and age. In order to address the effect of clustering at the
boundary, we consider censored multivariate normal and skew model. The
extended skew normal is used to model the selection due to drop-out.
--
Mario Cortina Borja; [log in to unmask]
Centre for Paediatric Epidemiology & Biostatistics
UCL Institute of Child Health, London WC1N 1EH, UK
Phone +44(0)20 7905 2113 Fax +44(0)20 7905 2381
You may leave the list at any time by sending the command
SIGNOFF allstat
to [log in to unmask], leaving the subject line blank.
|