StatsWAP2009July17

Mixed Effects Models in MRI Research

Summer Seminar Series: Statistics without the Agonizing Pain (WAP Series)
Time/Location: Friday, July 17, 2009 – 3 pm – 4 pm Clark Hall 314
Speaker: Yang An, National Institute on Aging - Intramural Research Program

Laboratory of Personality and Cognition - http://www.grc.nia.nih.gov/branches/lpc/lpc.htmv
Cognition section - http://www.grc.nia.nih.gov/branches/lpc/sresnick.htm

Mixed effects models (continuous outcomes) - also known as random effects models
Generalized estimating equations (discontinuous outcomes)

General topics

• Ordinary regression model - each data point comes from a separate "person" - L2 fit - Fixed effects
• ME model - each subject has its own slope. Find population slope.
• REML - restricted maximum likelihood -- preferred for model estimation. Not suitable for model comparison with differing random effects.
• Empirical Bayes (EB) for estimation of individual trajectories

Links about R

• Fitting Linear Mixed Models in R : http://cran.osmirror.nl/doc/Rnews/Rnews_2005-1.pdf#page=27
• (old way) Using R and lmer to fit linear mixed models with crossed random effects : http://www.stat.wisc.edu/~burgette/lme4-4.pdf
• (new way) Fitting Mixed-Effects Models Using the lme4 Package in R : http://www.stat.wisc.edu/~bates/IMPS2008/lme4D.pdf
• Tips on using mixed models in R: http://psy-ed.wikidot.com/glmm

Suggested Books

• Applied Longitudinal Data Analysis : http://books.google.com/books?id=DIlsijNIYtUC&dq=Applied+Longitudinal+data+analysis&printsec=frontcover&source=bn&hl=en&ei=pdVgSq6QNtTktgf2h4DoDA&sa=X&oi=book_result&ct=result&resnum=4
• Linear Mixed Models for Longitudinal Data : http://www.amazon.com/Linear-Mixed-Models-Longitudinal-Data/dp/0387950273
• Analysis of Longitudinal Data : http://www.amazon.com/Analysis-Longitudinal-Data-Peter-Diggle/dp/0198524846