[Statlist] talk on statistics

[Christina Kuenzli]

                  ETH and University of Zurich 

                           Proff. 
         A.D. Barbour - P. Buehlmann - F. Hampel - L. Held
                  H.R. Kuensch - S. van de Geer

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           We are glad to announce the following talk
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     Friday, October 19, 2007  15.15h  LEO C 6
 
     The effect of miss-specified baseline characteristics on
     inference for longitudinal trends in linear mixed models 
    
     Geert Verbeke, Biostatistical Centre K.U.Leuven, Belgium

The main advantage of longitudinal studies is that they can distinguish
changes over time within individuals (longitudinal effects) from
differences among subjects at the start of the study (baseline
characteristics; cross-sectional effects). 

Often, especially in observational studies, longitudinal trends are
studied after correction for many potentially important baseline
differences between subjects. We show that, in the context of linear
mixed models, inference for longitudinal trends is in general biased if
a wrong model for the baseline characteristics is used. However, we will
argue that this bias is small in most practical situations and
completely vanishes in the special  case of a growth-curve model for
complete, balanced data. In the latter case, inference for longitudinal
trends is completely independent of additional baseline covariates that
might have been omitted from the model. 
This work is joint with S. Fieuws.


________________________________________________________
Christina Kuenzli            <kuenzli using stat.math.ethz.ch>
Seminar fuer Statistik      
Leonhardstr. 27,  LEO D11      phone: +41 (0)44 632 3438         
ETH-Zentrum,                   fax  : +41 (0)44 632 1228 
CH-8092 Zurich, Switzerland        http://stat.ethz.ch/~